Braze- To solder with brass, an alloy made of copper and zinc.

Bridging- Bridging is the finding of a dimension by the testing of measurements spanning an unknown dimension and successively closing the distance between them until the unknown dimension is approximated.

Broach- To finish either an exterior or an interior shape of a workpiece using a cutting tool with a series of teeth that gradually increase as the tool is pushed or pulled.

Burnish- To smooth a workpiece by rolling or sliding it over a surface under pressure.

Burr- The ridge or raised edge left after a machining operation.

Bushing- A metal sleeve or lining that acts as a bearing between rotating or moving surfaces.

Caliper Measurement- The use of any instrument that can be set to the part feature being measured and then transfer that setting to a standard for comparison.

Callout- A note on the blueprint identifying a dimension, specification, or machining process.

Cam- A sliding or rotating part used to convert rotary motion into intermittent or reciprocating motion.

Carburizer- Heating a low-carbon partpiece to about 2000 degrees F (or below melting temperature in carbonaceous solids, liquids, or gases) and then allowing it to cool slowly in preparation for heat treatment.

Cartesian Dimension- A dimension between points which are parallel or perpendicular to each other (2-D or 3-D).

Case Harden- The process of hardening the outer surface of ferrous alloy by heating it to a critical temperature and then quenching in oil or water.

Centerline Average- See roughness average.

Centerplane- The middle or median plane of a feature.

Centralize- Movement of instrument by feel of contact so that its axis is oriented parallel to the line of measurement. This is sometimes called "rocking".

Chamfer- The flat surface formed by cutting off a sharp corner, usually at an angle of 45 degrees.

Chase- To cut thread in a lathe rather than with a die.

Circle- The circle is the standard for angular measurement. It consists of a closed, plane curve, all of whose points are equidistant from one enclosed point, the center. See also lobing and roundness.

Circularity- The condition on a surface of revolution (cylinder, cone, or sphere) where the points of the surface are intersected by any plane perpendicular to a common axis (cylinder, cone) or passing through a common center (sphere) equidistant from the center.

Circular Pitch- The length of the arc along the pitch circle from the center of one gear tooth to the center of the next.

Circular Runout- The composite control of circular elements of a surface independently at any circular measuring position as the part is rotated through 360 degrees.

Clearance Fit- A fit having limits of size so prescribed that a clearance always results when mating parts are assembled.

Clinometer- A clinometer is a very precise level.

Closed Loop- A system in which the output of one or more elements is compared to some other signal to provide an actuating signal to control the output of the loop.

Coaxiality- The condition that exists when two or more features have coincident axes (i.e., a feature axis and a datum feature axis).

Collimation- Collimation means to render parallel. Light rays emanating from a source diverge. A collimator directs them into parallel rays. See also infinity. An alignment collimator is a target using collimation.

Command Loop- An input signal or an external signal to which the servo must respond.

Comparator- Both indicators and comparators are sensing elements in systems that measure by comparison. The unknown is compared to a standard. Indicator is the term applied to the lower precision instruments such as dial indicators. Comparator is the term applied to the higher precision instruments. These may be either mechanical or electronic, but are chiefly electronic. For greatest reliability these instruments should be used only to compare, not to measure directly. Their greatest accuracy is at the zero reading. The further from zero, the greater the error they add. A test indicator is the least precise version, and is used only for rough setup, etc.

Comparison Measurement- Comparison measurement is measurement with an instrument that detects the difference between the part and a separate standard. See also direct measurement.

Complimentary Angle- See angle.

Component- A single unit or part.

Compound Angle- Compound angles are formed by the edges of triangles that lie in different planes. Face angles are formed by the intersections of edges of solids. Dihedral angles is the opening between planes.

Concentric- Having a common center, such as circles or diameters.

Concentricity- A condition in which two or more features (cylinders, cones, spheres, hexagons, etc.) in any combination have a common axis.

Constant Interval Sampling- Sampling based on the sequence at which parts leave a production operation.

Construct- To create new elements with previously measured or constructed elements.

Contour- The literal meaning of contour is the outside outline of any shape. In practice, however, it has come to mean the irregular outlines that cannot be conveniently defined by combinations of straight lines and area of regular radii.

Contour Tolerancing- See profile of a line or profile of a surface.

Control- A device used to regulate the function of a unit.

Control Charts- Charts that facilitate visual analysis of production trends. Each contains separate average chart and range chart.

Coordinates- A set of numbers uniquely defines a position or point in space.

Coordinate Measuring Machine- Coordinate measuring machines are instruments that locate point coordinates on three-dimensional structures while simultaneously integrating both the dimensional and orthogonal relationships. CMMs are chiefly used for plate work (q.v.) on relatively large parts. They are available in a large variety of sizes and configurations.

Cosine Error, Sine Error- The cosine error is induced by lack of squareness between the feature of the part and the measurement instrument. The sine error results from misalignment of a flat contact with the part feature.

Counterbore- The enlargement of the end of a hole to a specified diameter and depth.

Countersink- The chamfered end of a hole that receives a flat head screw.

Cylindricity- A condition of a surface of revolution in which all points of the surface are equidistant from a common axis.

DCC Position Point- To move the probe tip an absolute or incremental distance to a predetermined position through data input.

Datum- A point, line, plane, cylinder axis, etc., assumed to be exact for purposes of computation or reference and established from actual features. From the datum the location or geometric relationship of other features of a part may be established.

Datum Axis- The theoretically exact centerline of the datum cylinder as established by the extremities of contacting points of the actual datum feature cylindrical surface or the axis formed at the intersection of two datum planes.

Datum Feature- A feature (hole, slot, diameter, etc.) used to establish a datum. It refers to the actual part surface of the feature coincidental with or relative to a datum.

Datum Identification Symbol- The datum reference letter drawn in a rectangular box.

Datum Line- A line that has length but not breadth.

Datum Plane- A theoretical plane established by extremities of the actual feature with a reference plane.

Datum Point- A point that has position but not extent.

Datum Reference- A datum feature as specified on a drawing.

Datum Reference Frame- A system of three mutually perpendicular datum planes or axes established from datum features as a basis for dimensions for design, manufacturing, and verification. It provides complete orientation for the feature involved.

Datum Surface- A surface or feature (hole, slot, diameter, etc.) that refers to the actual part surface or feature coincidental with or relative to a datum and/or used to establish a datum.

Datum Target- A specified point, line, or area on a part used to establish a datum.

Decimal-inch System- The decimal-inch system is the customary inch-pound system in which the inch has been divided into decimals in order to avoid fractions that are awkward in calculations.

Dedendum- The radial distance between the pitch circle and the bottom of the tooth.

Degradation of Workmanship- Degradation of workmanship is the generalization that no part feature is as accurate as the process or machine that produced it. Thus, the less dependent a part feature is on previous operations, the greater the probability of accuracy.

Depth of Focus- Depth of focus depends upon the numerical aperture (N.A.) as well as the magnification and is inversely proportional to both. The higher the magnification the shorter the depth of focus for any given numerical aperture. Also known as depth of field.

Design Size- The size from which the limits of size are derived by the application of tolerance. When there is no allowance, the design size is the same as the basic size.

Detail Drawing- A drawing of a single part that provides all the information necessary for the production of that part.

Diascopic Projection- Diascopic projection is the term for projection of transparent objects, such as film. See also episcopic projection.

Die- A tool used to cut external threads by hand or or machine. Also, a tool used to form or cut a desired shape.

Die-Casting- A method of producing castings using molten metal under pressure and injecting it into a suitable steel mold.

Die-Stamping- A partpiece cut out by a die.

Digital/Analog- A digital instrument displays the measurement in numerals. In an analog instrument a moving member (a "hand") moves in proportion to the change in measurement, therefore it replicates the measurement, but greatly amplified. In general, digital readouts are desirable to show limits, whereas analog readouts are best when trends are to be followed. Most analog instruments use dial scales for readout.

Digital Readout- (DRO) – Interfaces scales/readerheads, interfaces probe to computer and displays X, Y and Z axis location relative to object or machine coordinate.

Dihedral Angle- The dihedral angle is the opening between planes. See also compound angle.

Dimension- A numerical value expressed in appropriate units of measure and indicated on a drawing.

Dimensional Metrology- See linear metrology.

Direct Measurement- Direct measurement is measurement with an instrument that incorporates its standard. See also comparison measurement.

Discrepancy- See uncertainty.

Discriminating Power- Measure of performance of sampling plans.

Discrimination- Discrimination is the fineness of the scale divisions of an instrument. It is the smallest division of the scale that can be read reliably. As discrimination is incresed the range is decreased. The ratio for this varies among the types of instruments.

Displacement Method- Displacement method is a method of measurement in which each end of the part feature is separate compared to a standard. There is a displacement in getting from one end to the other. It is the relationship between the distance displaced and the standard that constitutes the measurement.

Distance Dimension- Defines a distance between two elements as selected by the operator.

Dividing Heads- Dividing heads are mechanical devices for dividing a circle into angular portions.

Dowel Pin- A pin anchored in one partpiece and fitting into a hole in an abutting partpiece to prevent motion or slipping or to keep the pieces accurately located in the relative position.

Draft- The angle or taper on a molding pattern or casting that permits withdrawal from the mold or forming die.

Drill- To cut a cylindrical hole with a drill or a pointed tool rotated under pressure.

Drop-Forging- Formation of a partpiece between dies by the use of a drop hammer.

Dynamic Measurement- Most linear measurement is static. It is performed on something that is stable and unchanging, at least over a short period of time. Dynamic measurement, in contrast, is the continuous monitoring of a changing quantity. Although there are many exceptions, digital readouts are associated with static measurement and analog readouts are associated with dynamic measurement.

Eccentricity Error- Eccentricity Error is discrepancy in angular measurement caused by the measurement arc not being concentric with the center of rotation.

Element- A detail of a work piece: plane, circle, etc.

1 – D – Point

2 – D – Line, Circle, Eclipse

3 – D – Plane, Cylinder, Cone, Sphere

Elongated Hole- A hole that has been enlarged on two sides.

Enclosure- A rectangle drawn around a component to indicate the limits of an assembly.

End Standards- End standards are special gage blocks that are placed on ends of stacks of gage blocks to convert to other measurements than the normal external end measurements of the stacks.

Episcopic Projection- Episcopic projection is the term for optical projection of opaque objects. See also diascopic projection.

Error- Error is the difference between the measured value and the true value. Error always exists although it may not be measurable. Observational error is formed during the reading of an instrument. Parallax error is caused by apparent shifting of objects when the viewing position is changed. Manipulative error is caused by the handling of the instrument and the part. Bias error is the conscious or unconscious influencing of measurement. See also systematic error, random error and illegitimate error.

Execute Program- To run a program.

Extrusion- The process of shaping metal by forcing it in the hot or cold state through dies of the desired shape.

Face Angle- Face angles are formed by the intersections of edges of solids. See also compound angle.

Feather- A flat sliding key.

Feature- Specific characteristics of component portions of a part that may include one or more surfaces such as holes, threads, profiles, faces, or slots.

Feature Control Symbol- A rectangular box containing geometric characteristic symbols and the form or position tolerance.

Feature of Size- One cylindrical or spherical surface, or a set of two plane parallel surfaces, each of which is associated with a dimension. A feature such as a hole, shaft, pin, or slot that has an axis, centerline, or centerplane when related to geometric tolerances.

Feedback- Output signal from a feedback element.

Feel- Feel is the perception of the distortion that results from physical contact between the instrument and the part or standard.

Field of View- In an optical system the field of view is the screen diameter divided by the magnification.

File- A tool that has sharp cutting points or teeth used for abrading or smoothing other surfaces.

Fillet- A concave surface or filling at the intersection of two surfaces that provides added strength.

Fin- A thin projected edge or casting.

Finish- A surface specification.

Fit- The general term used to specify the range of tightness or looseness as a result of a specific combination of allowances and tolerances in the design of mating part features. There are four fits: clearance, interference, transition, and line

Flatness- The condition of a surface having all elements in one plane.

Folded Optics- Folded optics refers to the use of mirrors or prisms to realign optical paths so that instruments may be of compact size.

Form Tolerancing- Permitted variation from the perfect form indicated on the drawing.

Freedom- There are six possible degrees of freedom. Three are translational and involve movement in the X, Y and Z axes. The other three are rotational about these axes. If movement in any of these degrees of freedom is prevented it is said to be constrained. See also orthogonal.

Fringe Bands- Fringe bands are the alternate light and dark stripes that result when two rays combine and interference takes place.

Fringe Patterns- Fringe patterns are groups of fringe bands.

Fuller- A hammer used for forming grooves and spreading hot iron under hammer blows.

Full Indicator Movement- (FIM, FIR, and TIR): FIM refers to full indicator movement during one full revolution of the part about its datum axis. FIR refers to full indicator reading. TIR refers to total indicator reading.

Full Indicator Reading- (FIR, TIR, and FIM): The total indicator movement observed with the dial indicator in contact with the part feature surface during a full revolution of the part about its datum axis. (Use of the international term FIM is recommended.) Also refers to the reading observed while in traverse over a fixed noncircular shape.

Gage, Gauge- Gauge is the spelling used in Great Britain but finds some use in the U.S. It is chiefly found for nonlinear measurement instruments (fluid gages, etc.). However, it is finding increased use for coordinate measuring machines where it designates a device with a proportional range and some form of indicator.

Gages, Snap- A snap gage is a caliper type device that has been preset to a given dimension. Often made with two settings, one to admit acceptable parts, the other to reject out-of-tolerance parts. This general class is known as attribute gages and are frequently called "go and not-go" gages or "go/not-go" gages. They are also called "limit" gages. See also go/not-go gaging.

Gaging- Gaging is single-purpose measurement to determine if objects are between size limits or to sort objects into size categories.

Galvanize- To coat a metal surface with zinc as a protection against corrosion.

Geometric Characteristics- The basic elements that form the language of geometric dimensioning and tolerancing.

Geometric Dimension- A dimension between two elements which takes into consideration the specific conditions of an element.

Geometric Optics- Geometric optics is the technique for ray tracing. See also ray tracing.

Go/Not-Go Gaging- A go gage accepts all properly sized parts. If a female part is not accepted it is too small. If a female part is accepted by the not-go gage, it is too large. The reverse applies to male parts. See also snap gages.

Graduate- To mark in regular degrees of measurement, as on a scale or dial.

Grinding- A machine operation that consists of finishing a metal surface by means of abrasives.

Gusset- An angular piece of metal fastened to reinforce or strengthen a partpiece or assemblies.

Hardness Test- Techniques used to measure the degree of hardness of heat-treated materials.

Heat Sink- A heat sink is a body with rapid heat transfer on which workpieces and gages can be placed to arrive at the same temperature before measurement. The process is known as "normalizing". See also temperature.

Heat Treatment- The application of heat to metals to produce desired qualities of hardness, toughness, or softness.

Histogram- Graphical representation of a frequency distribution in which one dimension is proportional to the range of frequencies and the other dimension is proportional to the number of frequencies appearing within the range. See also normal distribution curve.

Hobbing- A special gear-cutting process in which the gear blank and hob rotate together as in mesh during the cutting operation.

Home Position- Defines absolute zero-location relative to machine coordinates.

Hone- A method of finishing a hole or other surface to a precise tolerance.

Horizontal- See vertical.

Hub- The central part of a wheel.

Implied Datum- An unspecified datum whose influence on the application is implied by the dimensional arrangement on the drawing (e.g., the primary dimensions are tied to an edge surface, and this edge is implied as a datum surface and plane).

Inch-Pound System- The inch-pound system is the conventional measurement system for the United States and Great Britain. Based on the foot, pound, second, degree Fahrenheit, ampere and candela.

Incremental System- A system of numerically controlled machining that refers to the preceding point when making the next movement.

Index Heads- Index heads are mechanical devices for dividing a circle into angular portions. Also known as dividing heads.

Indexing- Indexing is the act of measurement of angles or setting out angles for machining by use of a rotary table.

Indicators- See comparators.

Infinity- In metrology infinity has a special meaning. It is the distance from which rays reaching the observer are parallel. See also collimation and zenith sight.

Inspection- Inspection is the verification of conformity to a standard, generally applied to the production of goods, but also used for remedial examination.

Interchangeability- The condition that ensures the universal exchange of a mechanism or assembly.

Interchange Method- The interchange method is a method of measurement in which both ends of the unknown feature are compared with both ends of a standard of the desired dimension, or to a ruled scale. It is known as measurement by comparison.

Interference Fit- Interference fit refers to parts that must be compressed to mate.

Interferometer- An interferometer is any instrument making an application of interferometry. See also interferometry.

Interferometry- Interferometry is the formation of visible bands of light by interacting wave fronts. Interferometry is used for precise comparisons using gage blocks and for surface evaluation. Interferometry is also the basis for precise optical metrology instruments such as the pointing interferometer.

Intermediate Point- A position point in a DCC program to assure probe tip path clearance between two measured points.

International Inch- The international inch is the reconciliation of the inch to the meter. One inch equals 25.4mm.

Interpolation- Interpolation is the selection of the nearest graduation when a measurement lies between. The observational equivalent to the rounding off (q.v.) process in computation.

Interrelated Datum Reference Frame- A reference frame that has one or more common datums with another datum reference frame.

Involute- A spiral curve generated by a point on a chord as it unwinds a circle or a polygon.

Jig Transit- A jig transit is similar to a surveyor’s transit, but it does not have scales for measuring angles. It has, however, provisions for both autocollimation (q.v.) and optical projection. Its most important feature is that the elevation axis is hollow. This allows two lines of sight perpendicular to each other to intersect on the azimuth (q.v.) of the instrument. Also known as optical transit square and jig level. See also tachymetry.

Johansson, C.E.- Johansson was a pioneer in metrology and clearly anticipated modern, interchangeable gage blocks. More importantly, he understood the significance of this development.

Joy Stick Control- A joy stick control allows the operator to control the direction of travel of the moving member in two orthogonal axes, as well as the rate of travel. It is regularly used for manual operation of CMMs. See also coordinate measuring machine.

Ket- A bar, pin, or wedge used to prevent rotation of a gear or pulley on a shaft.

Keyseat- The groove that holds the key in position, as in a shaft.

Knurl- The process of marking the surface of a part by rolling depressions in the surface, usually for better hand grip.

Krypton 86- Krypton 86 is a gas which, when electrically excited, emits the wave length of light which is the basis for the international standard. It was selected because of its stability. However, it is more practical to use helium gas to emit light for most practical work.

Lap- To finish a surface with a very fine abrasive impregnated in a soft metal.

Laser- A laser emission is an intense, narrow beam of light that is of a single wave length (color). The beam will travel great distances with little loss of energy and only small dispersion. Warning: A laser beam can damage eyesight or blind. Never look directly into the beam. Laser instruments are similar to conventional ones except for the laser light source and the use of photoelectric sensors. See also photoelectric instruments.

Layout- Layout is the use of measurement instruments to mark features on workpieces for subsequent machining. Limited to rough machining, the final machining is controlled by machine control settings and verified by measurement.

Least Count- The least count is the discrimination of a vernier instrument.

Least Material Condition (LMC)- The condition of a part feature that contains the least amount of material possible (e.g., largest hole size and smallest shaft size).

Level- The level is an instrument for establishing a horizontal line. By means of two or more such lines intersecting, a horizontal plane may be established. The standard for a level is gravity. Very precise levels are known as clinometers.

Light- Light is the electromagnetic energy radiation in frequencies to which the human eye is sensitive, as well as those of slightly longer and slightly shorter wave lengths. See also light rays and ray tracing.

Light Rays- Light rays are imaginary lines perpendicular to wave fronts. Althought they do not physically exist they are a convenience in tracing the passage of light through an optical system. See also rays and ray tracing.

Light Wave- A light wave is the pulsation in space that transmits light energy. A wave front is an advancing pulse of energy. See also light.

Limit Dimensioning- A method of dimensioning in which only the maximum and minimum dimensions are specified.

Limiting Constants- Factors for determining control limits.

Limiting Quality Protection- The worst quality that can be accepted.

Limits of Size- The applicable maximum and minimum sizes of a feature.

Line of Collimation- See line of sight.

Line Fit- A fit having limits of size so prescribed that surface contact may result when mating parts are assembled.

Line-of-Sight-Telescope- In practical work the point on the object being examined at the intersection of the reticle’s lines is on a line called line of sight or line of collimation. It is absolutely flat and straight in undisturbed air. It may be used as a reference rom which measurements are made. The simplest optical alignment instrument is the line-of-sight telescope. This type of telescope establishes optical lines of reference. With optical micrometers they provide a limited measuring range. With the addition of the micrometers these instruments become known as alignment telescopes. See also optical micrometers.

Linear Metrology- Linear metrology is related to measurements taken along a line. In general use it includes measurement along curved lines as well as straight lines and angles. It applies to areas and volumes because these can be reduced to their component lines. Often referred to as dimensional metrology.

Lobing- Lobing is deviation from roundness. It is to a round surface what waviness is to a flat surface. See also roundness.

Location Tolerance- A statement of how far an actual feature may vary from the perfect location implied by the drawing as related to datums or other features. Expressions of location tolerances refer to the category of geometric characteristics containing position, concentricity, and symmetry.

Logarithms- The term logarithms is generally used to mean "common logarithms". These are the exponents to which ten must be raised to equal the number. For example, the logarithm of 100 is 2 because 10 sq. = 100. The logarithm of 23 is 36173 because 10 .36172 = 23. Logarithms facilitate the expression and calculation of complex values.

LURD- LURD is a convention for expressing measurement changes to minimize misunderstandings. It stands for: left, up, right, down.

Macrogeometry- Macrogeometry means large scale consideration of form or shap. In popular usage macrogeometry is concerned with size and shape that can be expressed with standard inspection instruments. Evaluation of squareness in shop machines usually is macrogeometry.

Macrometrology- Macrometrology refers to large scale work such as the setup of large machinery, ship building, land surveying, etc. See also macrogeometry.

Magnification- The total magnification is the product of the eyepiece magnification and the objective magnification. The eyepiece magnification is usually X10. Thus coupled with an objective of X43 the total magnification would be 430 power.

Manipulative Error- Manipulative error is error caused by the handling of the instrument and the part. See also error.

Margin of Safety- In a measurement it means the amount that the measurement process exceed the required minimum accuracy and/or precision.

Master Flat- A master flat is an optical flat having surfaces of maximum precision. It is used to calibrate working flats. See also optical flats.

Mastering- Mastering means setting to standards. Although it can apply to all types of measuring systems it is chiefly applied to pneumatic metrology.

Material Condition- An outside edge is less than 180 degrees of material. An inside edge is more than 180 degrees. These are the material conditions. When material is dimensioned the part feature is male. When the space between material is dimensioned the part feature is female.

Maximum Dimension- The largest acceptable limit.

Maximum Material Condition (MMC)- The condition of a part feature that contains the maximum amount of material possible (e.g., minimum hole size and maximum shaft size).

Maximum True Position- The condition of a part feature at MMC located at the limit of the specified true position tolerance one. It represents the worst condition of assembly.

Measure- An element of reference used for quantitative comparison.

Measured Point- The measured point is the point on a scale that coincides with the end of the feature being measured opposite from the reference point. See also reference point.

Measurement- Measurement means to proportion by measured lots. The measurement may be any quality (length, weight, hardness, ertc.) and lots may be in any units (inches, volts, picas, etc.) See also metrology.

Measuring Speed- The speed or velocity by which the probe approaches an element about to be contacted.

Median Plane- The middle or centerplane of the feature.

Memory Device- A memory device is a means for retaining a reading mechanically so that it will not be lost. Usually a simple clamp. The term is also used for the memory capability of some electronic measurement instruments.

Metric System- The familiar name for System International d’Unites, the most recent of many so called metric systems. Often abbreviated "St." Based on the meter, kilogram, second, degree Celsius, ampere and candela.

Metrology- Metrology is the science of measurement. See also measurement.

Metrology Laboratory- A metrology laboratory is a laboratory for the calibration of standards. May be a department within a company or an outside service.

Microgeometry- Microgeometry means small scale considerations of form or shape. The precision in microgeometry is expressed in mikes. Evaluation of surface finish and flatness of gages is microgeometry.

Micrometer Instruments- Micrometer instruments are measurement instruments that achieve their amplification as a result of the resolution of screw threads.

Micrometrology- Micrometrology refers to very small work, smaller than encountered in most shop work. See also microgeometry.

Microscope- A microscope is an instrument for greatly enlarging the view of a part feature. That capability is known as amplification (q.v.). Whereas most measurement systems alter their measurements to a considerable degree, optical systems do not impose those limits, but they have other problems.

Mike- In the decimal-inch system of terminology, mike means millionths. However, in popular use "micro-inch" (with or without hyphen) is the most common designation for millionths of an inch.

Mil- In the decimal-inch system of terminology, mil means thousandths.

Mil-STD-105- The standard for sampling required for most Department of Defense applications.

Minimum Dimension- Opposite of maximum dimension.

Minimum Material Condition- See Least Material Condition. See also tolerance.

Modifier- The term used to describe the application of the MMC or the RFS principle.

Monochromatic Light- Monochromatic light consists of one wave length (color) only.

Multiple Datum Reference Frames- More than one datum reference frame on one part.

National Bureau of Standards (NBS)- Former name for National Institute of Standards and Technology, the official standardization agency for the government of the United States.

Natural Capability- The natural capability of a process is range of the resulting part sizes that can be expected during normal operation. It is the basis for statistical quality control by variables (q.v.).

Natural Functions- See trigonometry.

Nominal Size- The stated designation used for general identification.

Nonferrous- Not derived from an iron base or an iron alloy base (e.g., aluminum, magnesium, and copper).

Normal- Probe tip direction is perpendicular to the element being probed.

Normal Distribution Curve- The normal distribution curve is the bell shaped curve that results when a variable is changing by chance, such as the throws of dice. It is called a histogram. In the same manner any production process may be graphed. See also standard deviation.

Normality- See perpendicularity.

Normalize- See heat sink and temperature.

Normalizing- A process in which ferrous alloys are heated and then cooled in still air to room temperature to restore the uniform grain structure free of strains caused by cold working welding.

Numerical Aperture (NA)- The higher the NA the greater the resolving power (q.v.) The NA is = n sin u where n is the lowest refractive index that appears between the objective and the front lens of the objective, and is half of the angular aperture of the objective. Fortunately, it is marked on lens mounts.

Observational Error- Error formed during the reading of an instrument. See also error.

Off-Axis Error- When measuring a curved surface, the true value is found only when the measuring axis is in line with the center of curvature. Any deviation is called off-axis error.

Operating Band- The acceptable range based on the standard values.

Operating Characteristic Curves- Operating characteristic curves are a graphical means for comparing sampling plans. They enable SQC plans to be compared. They show the relationship between lot size and number of defectives.

Operator Text- Text output to screen only as instructions for the operator.

Optical Alignment- Optical alignment is that branch of metrology that uses light waves to examine sizes and geometrical relationships over larger distances than ordinarily required in shop and laboratory work.

Optical Comparator- An optical comparator is an instrument that projects a greatly magnified image of a part feature onto a screen for examination.

Optical Flat- An optical flat is a glass or quartz reference surface with one or both sides finished to be precisely flat and to have minimum surface imperfections. Flats is the general term for such devices made from nontransparent materials such as steel or ceramics. A master flat has surfaces of maximum precision. It is used to calibrate working flats.

Optical Micrometer- An optical micrometer is a mechanically adjustable means to offset an optical path in one axis. It is calibrated so that the offset may be known. Optical micrometers are frequently used in pairs at right angles to each other. They are not used alone but are incorporated into instruments such as the line of sight telescope. Note that the optical micrometer does not affect the angle of the optical path, only its displacement.

Optical Polygons- Optical polygons are polygons with precisely spaced faces that represent divisions of a circle. In other words, they represent angles. They are used with optical alignment instruments to set out and to measure angles.

Optical Square- An optical square is a means for turning all or some of the rays in the optical path to 90 degrees from that path.

Orientation Tolerances- Tolerances applicable to related features where one feature is selected as a datum feature and the other is related to it. Orientation tolerances are perpendicularity, angularity, and parallelism.

Orthogonal- Orthogonal literally means rectangular or right angled. In popular use it has come to mean movement in two or three axes at right angles to each other.

Orthogonal Array- Orthogonal array refers to a device in which the functional parts act at right angles to each other.

Orthographic Projection- A multiview drawing that shows every feature of a partpiece in its true size and shape.

Overhang- The unsupported portion of an instrument. Always to be avoided.

Parallax Error- Parallax error is apparent shifting of objects when the viewing position is changed. See also error.

Parallel Separation Planes- Parallel separation planes are a concept that simplifies measurement with optical flats. The concept consists of a set of planes parallel to the working surface and one-half wave length apart. Their intersection with the part is seen as fringe bands.

Parallelepiped- The shape of a tolerance zone. The term is used to describe total width and to describe geometrically a square or rectangular prism or a solid with six faces, each of which is a parallelogram.

Parallelism- The condition of a surface, line, or axis equidistant at all points from a datum plane or axis.

Perpendicularity- The condition of a surface, axis, or line 90 degrees from a datum plane or a datum axis.

Photoelectric Instruments- In order to avoid the subjective bias of the observer, opotical instruments have been developed that use photoelectric sensors to ascertain the reference and measured points. The most advanced of these use lasers as their light source. See also laser.

Pilot Hole- A small hole used to guide a cutting tool for making a larger hole.

Pinion- The smaller of two mating parts.

Plan View- The top view of a partpiece.

Plate Work- See surface plate.

Pneumatic Metrology- Pneumatic metrology refers to any measurement system that uses pressure changes in a fluid (air or other gases) system to amplify changes in part sizes or shapes. Pneumatic gages are basically analog devices.

Polar Chart Method- See V-block method.

Polar Dimensions- A dimension defined by distance and an angle.

Position- Defines a dimension of one element as selected by the operator relative to the active alignment system part zero.

Positional Tolerancing- Positional tolerancing recognizes that the limits of clearances and fits between parts occur in circles, not the rectangles that result from tolerancing with orthogonal relationships (q.v.). This allows tolerances to be widened without loss of reliability. See also tolerance.

Positioning Speed- The speed of the probe tip as it traverses between probe-speeds.

Precision- Precision refers to the fineness of readings or dispersion of measurements. Precisiion is a positive matter, whereas accuracy is comparative and reliability is relative.

Precision Instruments- Precision instruments are those providing amplification of the natural sense of sight and touch.

Primary Alignment- Levels the part. Defines spatial orientation of the part.

Print Text- Comments or explanations inside a program to clarify dimensions.

Probe Head- An intricate assembly which carries the touch probe and probe tips and attaches to the Z-axis assembly.

Probe Point Deviation- Defines the location of a measured point relative to a geometrically perfect form numerically.

Probe Speed- The speed of the probe tip as it approaches an element about to be contacted.

Probe System- An assembly of one or more probe tips.

Probe Tip- A single element of a probe assembly which is used to touch the surface of a feature on the part.

Profile- To machine an outline by moving a small rotating cutter usually controlled by a master cam or die.

Profile of Any Line- The condition permitting a uniform amount of profile variation, either unilaterally or bilaterally, along a line element of a feature.

Profile of Any Surface- The condition permitting a uniform amount of profile variation, either unilaterally or bilaterally, on a surface.

Profile Tolerance- Tolerance that controls the outline or shape of a part as a total surface or at planes through a part.

Program- A sequence of steps which the computer can follow to do a task.

Projected Tolerance Zone- A tolerance zone applied to a hole in which a pin, bolt, screw, etc., is to be inserted.

Protocol- Printed results of dimensions.

Protractor- A protractor is an instrument for measuring angles by the displacement method. They usually have calibrated arcs as standards.

RMS- RMS is the abbreviation for root mean square. The RMS is the average of the squares of the deviations of the high and low values. Compare with AA.

Random Errors- Random errors result from erratic malfunctions of any part of the measurement system including the observer. For example, a loose element that may unpredictably change positions could add errors. Random errors are often found by the discrepancies when a measurement act is repeated. Random errors are also known as accidental errors. See also errors, systematic errors and illegitimate errors.

Random Number Table- A random number table is a table of numbers in which there is no discernable pattern of occurrences.

Random Sample- A random sample is the selection of a sample without bias. See also sampling.

Range Chart- A range chart is that portion of a worksheet (q.v.) showing the range of the samples.

Ray- A ray of light is an imaginary line perpendicular to a wave front (q.v.). See also light rays.

Ray Tracing- Ray tracing is the study of optical systems by means of rays.

Readability- Readability is the relative ease with which the measurement can be distinguished. For example, both a plain micrometer and a vernier caliper have the same discrimination, but the plain micrometer is more readable.

Real Image- A real image is the image formed by light rays from an object passing through a convergent (convex) lens. The real image lies on the side of the lens away from the object and is inverted. See also virtual image.

Ream- A machine operation consisting of enlarging a hole slightly to a close tolerance.

Reciprocation- A straight-line, back-and-forth motion or oscillation.

Reference Dimension- A dimension used only for information. It does not govern production or inspection.

Reference Plane- The reference plane is the plane in which the reference points lie. It is always perpendicular to the line of reference. The reference plane by definition must be flat. The reference plane is also known as the datum plane. See also flatness and surface plate.

Reference Point- The reference point is the position on a part feature from which a dimension is expressed. Usually, but not necessarily, it is expressed as zero. See also measured point.

Reflection- Reflection is the change of direction of light when it is directed upon a suitable surface.

Refraction- Refraction is the change in path when light passes from one transparent medium into a different medium.

Regardless of Feature Size (RFS)- The condition in which tolerances of position or form must be met irrespective of where the feature lies within its size tolerance.

Reliability- The reliability is the probability of achieving desired results. Reliability is a relative matter whereas accuracy is comparative and precision is positive.

Relief- A slight variance in the dimension of a machine part to allow for clearance.

Repeatability- Repeatability is the variation among several measurements taken with one instrument on one part feature. It is a test of precision, not of accuracy.

Resolution- Resolution is the ability to visually distinguish with the unaided eye between separate items, usually lines. It is the ratio of the width of one scale division (one output unit) to the width of the hand (the read-out element). Resolution is not the same as readability.

Resolving Power- The resolving power is the property by which small elements are distinctly separated., For practical work this is more important than the magnification. The measure of resolving power is numerical aperture (q.v.).

Reversal Technique- The reversal technique or reversal process is method for detecting or canceling small changes by comparing a variable with itself but with reversed algebraic sign.

Right Hand Rule- A method to define positive and negative vector directions in space.

Rivet- A metal pin with a head, used to secure two or more pieces.

Rotate- To turn an alignment system about one or more of its axes.

Roughness Average- The roughness average is the arithmetic average (AA) of the absolute values of the profile height deviations. It is sometimes referred to by its earlier term, centerline average (CLA). This is the method standardized for use in the U.S. Many other methods are also used and some ten have been standardized for use in other countries. See also lobing and V-block method.

Round Down- Round down is to leave intact the next remaining decimal place when rounding off a numeral five in last place.

Round Off- Round off is to arbitrarily eliminate the last decimal place.

Round Up- Round up is to raise the next remaining decimal place when rounding off a numeral five in last place.

Roundness- Roundness is the characteristic that all parts of a circle are identical. See also lobing.

Ruby Stylus- A specific type of probe tip made with a synthetic ruby ball.

Rule- See scale.

Runout- The deviation from the desired form of a part surface of revolution detected during full rotation of the partpiece on a datum axis.

Runout Tolerance- The distance an actual surface or feature is permitted to deviate from the desired form implied by the drawing during full rotation of the part on a datum axis. There are two types of runout: circular and total.

Sampling- Sampling is the procedure for removing a representative cross section of parts from a larger quantity. Random sampling refers to the fact that to be useful for statistical quality control (q.v.), the sample must not be biased. The method must assure that any part has as much or as little chance as any other one of being selected. Sampling plan is a formal adoption of a sampling schedule. See also statistics.

Sampling Plan- See sampling.

Sampling Table- A sampling table is a table that enables the samling to be planned based on lot size and AQL,

Sandblast- To remove surface scale by blowing a grit material against it at very high air pressure.

Scale- A high precision glass bar with incremental lines and spaces used to define distances very accurately.

Secondary Alignment- Defines rotational location of an object relative to its own elements or geometry. One of the other two axis which is not primary.

Section- A cross-sectional view at a specified point of a part or assembly.

Sensitivity- Sensitivity is the minimum input that results in a discernible output.

Sensor- A device that converts physical conditions into information so that the control system can understand the commands.

Serrated- Condition of a surface having sharp teeth.

Sexagesimal System- The sexagesimal system is a measurement system based on the number 60. Although there are other measurement systems for angles, the sexagesimal system predominates. Example: Circle = 360 degrees; Degree = 60minutes (60’), Minute = 60 seconds (60").

Shaper- A machine tool used to machine surfaces by a backward and forward motion (reciprocating ram).

Shear- To cut material by placing it between two steel blades and exerting a force.

Shewhart Control Charts- Shewhart control charts are a formalized method for collection and presentation of production data.

Shim- A piece of thin metal used between two parts to adjust the fit.

Significant Figures- Significant figures or digits are digits that begin with the first digit to the left that is not zero and end with the last digit to the right that is correct. 0.000543 significant figures approximation

Sine Bar- A sine bar is a bar to which two identical cylinders are attached with a known separation and a know relation to the reference surface of the bar. The bar becomes the hypotenuse of a triangle for angle measurement. See also sine plate and sine table.

Sine Plate- A sine plate is a ide sine bar. Sine block is another name for sine plate

Sine Table- A sine table is a sine device incorporated into the work table portion of an inspection device or machine tool.

Size Tolerance- The distance an individual feature or features may vary from the desired size. Size tolerances are specified with unilateral, bilateral, or limit tolerancing methods.

Soft Face- A machine operation on the surface of a part that provides a flat bearing surface for a washer, nut, bolt, or rivet head.

Specification- A detailed description of a part of material giving all information not necessarily shown on the graphic portion of the blueprint.

Specified Datum- A surface or feature identified with a datum feature symbol. See datum feature symbol.

Squareness- Squareness refers to a condition of being at a right angle to a line or plane. Also, a right angle in material form. See also perpendicularity.

Stage- For optical instruments such as the microscope and optical projector, stage is the term that corresponds to work table for most other instruments.

Standard- A standard is an agreed upon unit for use in measurement such as meter, pound, lumen, etc. The standard is the ultimate embodiment of the unit of length. A standard is a copy that is traceable back to the national standard.

Standard Deviation- The standard deviation is obtained by mathematically adjusting the data. It is expressed by the Greek letter sigma. It is the square root of the mean average of the squares of the deviations of all of the individual measurements from the mean average value X. See also normal distribution curve.

Standard Values- Standard values are representative values based on the experience record of the process.

Statistical Quality Control (SQC)- Statistical quality control, abbreviated SQC, refers to control of production by statistical methods (q.v.). SQC by attributes is based on go/not-go principles (q.v.). SQC by variables is the reverse. It is based on the natural capability (q.v.) of the process.

Statistics- Statistics is a branch of mathematics. It is concerned with the collection of data involving a number of occurrences, the analysis of the data, and the presentation of conclusions based on the analysis.

Straightness- A condition in which an element of a surface or axis is a straight line.

Stratified Sampling- Stratified sampling is the sampling of the same part produced in different lots.

Stress Relieve- To heat a part to a desired temperature, hold the temperature for a predetermined time, and then cool the part gradually in air. The process reduces internal stresses.

StylusMethod- The stylus method for surface examination resembles playing a phonograph record. A very small, smooth member (the stylus) is drawn along the surface. Its movement is amplified and recorded. The recording is usually a paper tape which can subsequently be analyzed.

Supplementary Angle- See angle.

Surface Datum Instruments- See true-datum instruments.

Surface Metrology- Surface metrology, also known as topology, refers to surface finish and geometry (flatness, roundness, etc.)

Surface Plate- The primary purpose of a surface plate is to provide a reference plane. It must also provide an adequate and convenient surface for the support of the part and the instrumentation. Plate work is layout and inspection performed from a surface plate.

Surface Roughness- Surface irregularities measured in microinches.

Surface Texture Specimens- Two types of specimens are in use. The most familiar is used to make visual comparisons with surface being examined. These are called roughness comparison specimens or pilot specimens. There are also precision reference specimens. These are used to calibrate the inspection instruments by comparison.

Symmetry- A condition in which a feature or features are symmetrically disposed about the centerplane of a datum feature.

Systematic Error- A systematic or constant error is an error that occurs in all readings uniformly. It may thereby go unnoticed.. It may be caused by any element in the measurement system, including the observer. For example, measurements to mikes in any temperature other than 68 degrees will contain systematic errors. Systematic errors are not revealed by repetition as are most other errors. See also errors, random errors and illegitimate errors.

Tachymetry- Tachymetry refers to the determination of distances and angles at distances by remote means, as in surveying. The theodolite is used for tachymetry. It is essentially a jig transit with scales for angle measurement. See also jig transit.

Tangent- A line drawn to the surface on an arc or circle so that it contacts the arc or circle at only one point.

Tap- A tool used to produce internal threads.

Target- In optical metrology a target is literally the feature that is viewed. This is often a graduated scale so that differences may be detected and measured.

Telescope- The telescope and microscope are similar in that a real image (q.v.) formed by a lens can be treated as if it were the actual object being observed; ile., it can be magnified or reduced and shape and dimensions examined. See also macrometrology, micrometrology and microscope.

Temper- To relieve hardness by reheating a metal to make it tougher and more ductile.

Temperature- Nearly all engineering materials change size when their temperature changes. Most increase their size. When measuring to tenth-mil or finer increments this becomes an important consideration. The measurement should be performed at 68 degrees F or the results corrected for the ambient temperature. Ambient temperature means surrounding temperature, i.e., air temperature. It must be remembered that it takes some time for items of different temperatures to normalize when brought together in ambient air. Normalize refers to arriving at the same temperature. See also heat sink.

Tensile Strength- The maximum load a piece can support without breaking or failure.

Ten-to-One Rule-The ten-to-one rule is a rule for enhancing measurement reliability. It states that the instrument should be able to divide the part tolerance into ten parts. It is often written as "one-to-ten" rule and spoken of as the "rule of ten". Modern statistical quality control procedures provide better methods for instrument selection and production control. However, the ten-to-one rule is recommended whenever statistical method are not available.

Terminal Line- A terminal line is the measured line when two intersecting lines form an angle. The vertex is the intersection of these lines.

Theodolite- See tachymetry.

Tolerance- The total amount by which a specific dimension may vary; the difference between upper and lower limits.

Tool Room Chart Gage- Tool room chart gages are transparent overlays that are placed on the screens of optical projectors. They provide various combinations of angles, arcs and radii for direct measurement of part features projected onto the sscreens.

Torque- The rotational or twisting force in a turning shaft.

Total Indicator Reading- The full indicator reading observed with the dial indicator in contact with the part feature surface during revolution of the part about its datum axis. Also refers to the total reading observed while in traverse over a fixed noncircular shape. (Use of the international term FIM is recommended, ANSI Y14.5M-1982.)

Total Runout- The simultaneous composite control of all elements of a surface at all circular and profile measuring positions as the part rotated through 360 degrees.

Touch Trigger Probe- A sensitive deflecting device which is used to register an X,Y,Z location when probe tip touches a feature part.

Taceability- Traceability refers to the ability to verify each successively higher step of calibration until the NIST (q.v.) international standards are reached.

Tracer Technique- The tracer technique is a technique for optical comparator measurement that utilizes a tracer that is moved along a feature to be inspected. The tracer simultaneously moves a similar member in the optical path so that its travel can be compared to the ideal path on a chart. This is useful when the feature to be examined cannot be placed directly in the optical path. That often occurs for inside features.

Transition Fit- A fit having limits of size so prescribed that either a clearance or an interference may result when mating parts are assembled.

Translate- To move the datum or zero point on a part to a new location.

Translation- Translation refers to motion without rotation, hence to linear motion. In measurement it refers to the comparison of an unknown dimension to a known standard.

Trigonometry- Trigonometry is the branch of mathematics dealing with the relationships of sides of triangles to the angles formed by them. Trigonometric functions are the ratios of pairs of triangle sides. They are useful to designate angles. Natural functions are tables of trigonometric functions divided out into decimals.

True-Datum Instruments- With a true-datum surface inspection instrument, a stylus is drawn across the surface guided by a true line. This line is incorporated in the instrument and is the standard. The graph shows deviations from that line. With a surface-datum inspection instrument the stylus is guided by a member that rests on the surface undergoing inspection. The member resting on the surface may be either a skid or a shoe.

True Position- Term used to describe the perfect (exact) location of a point, line, or plane (normally the center) of a feature in relationship to a datum reference feature.

Typical (TYP)- Term indicating that the dimension or feature may appear in more than one location and will be identical in size and configuration.

Under Control- Under control is the expression that signifies that the process is within tolerances.

Unilateral Tolerance- See tolerance.

Unit of Length- The unit of length is the arbitrary smallest whole division of a standard of length. See also standard.

Variable- A variable is a characteristic that can be expressed in numerical values from a continuous scale. Implies measurement.

Vector Direction- The direction in which a probe tip is leaving a point of contact.

Vernier Instruments- Vernier instruments are only those instruments in which the vernier is the outstanding characteristic. Many instruments not so classified use vernier scales to increase their amplification.

Vernier Scale- A vernier scale is the amplifying scale that has one division more in a given length than the main scale.

Vertex- See terminal line.

Vertical- Vertical literally means at right angles to the plane of the horizon. In metrology this is altered to state that it is in the direction of the pull of gravity. Horizontal is any line or plane at right angles to the vertical axis. For convenience, the X and Y axes are usually considered to be in the horizontal plane and the Z axis in the vertical. See also orthogonal array.

Virtual Condition- The collective effect of size, form, and location error that must be considered in determining the fit or clearance between mating parts or features. A derived size generated from the profile variations permitted by the specified tolerances. It represents the most extreme condition of assembly at MMC.

Virtual Image- A virtual image is the image formed by light rays from an object passing through a divergent (concave) lens. The virtual image lies between the lens and the object and is erect. See also image.

Virtual Size- The effective size of the profile that must be considered in determining the clearance between mating parts or feature.

Wave Front- A wave front I an advancing pulse of energy.

Waviness Height- Surface irregularities spaced too far apart to constitute roughness. Both height and width of waviness are identified and rated in inches.

White Light- White light is made up of a combination of colored light wave lengths. It varies according to its source.

Work Sheet- A work sheet is a form used to record inspection data for SOC (q.v.) by variables.

Wring- To wring is to bring two surfaces of micro-inch flatness together so that they adhere with only micro-inch separation. Wringing interval is the space by which two wring surfaces are separated. It varies but is in microinches. The air or liquid separating wring surfaces is known as film.

Wringing Interval- See wring.

Zenith Sight- A zenith sight is that point directly above the point of reference at infinity. See also infinity.

Zero of Ignorance- The zero of ignorance is an unnecessary division of a dimension. The additional zeroes usually result from ignorance, having been added to make all values in a table or discussion come out neatly to the same length. However, they are sometimes added fraudulently to make work appear more precise than it is. For example, in 0.57000 in the last two zeroes are the zeroes of ignorance when the actual value is 0.570.