Glossary

DATUM

In metrology, a datum is simply an idealized reference feature from which another features’ orientation, position, or other characteristic is defined. Datums can be many types of features, planes, cylinders, points, centerlines, constructions or offsets from other features, anything that can be measured or established for use in locating other features. Although the plural form of datum is really data, many people, including the author, uses datums as the plural in this application.

DATUM FEATURE

A datum feature is the measured or contacted feature which establishes a datum. It is an actual point, line or surface on the part being measured.

DIMENSIONAL INSPECTION

The process of characterizing an object’s size and shape through measurements of points, lengths, and volumes. Usually such an inspection results in a report comparing the measured object to another object, an idealized object, or a previous state of the object.

DIMENSIONAL INSPECTION

A method that involves measuring a part’s dimensions by way of a 3D laser tracker or scanner. There are several types of dimensional inspection services depending on the type of measurements that a project requires. Services offered by ECM: First Article Inspection, In-Line and In-Process Testing, As-Built Inspection as well as Calibration and Certification of machines, tooling and fixtures.

DIMENSIONAL METROLOGY

The study or practice of high precision measurements to quantify physical sizes, orientations, and distances of objects and shapes.

DISCRIMINATION THRESHOLD

The largest change in a value of a quantity being measured that causes no detectable change in the corresponding indication. NOTE: Discrimination threshold may depend on, e.g. noise (internal or external) or friction. It can also depend on the value of the quantity being measured and how the change is applied.

GAGE R&R (GAGE REPEATABILITY AND REPRODUCIBILITY)

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GANTRY CMM

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GD&T

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