Optical comparators are
devices that project a magnified image of
a part profile onto a screen where it is
compared to a standard overlay or scale.
Optical comparators are used for complex
parts, and parts that are otherwise hard
to measure. The profile of screw thread
is a typical example of a feature that lends
itself to optical comparison.
In addition to dimensional readings optical
comparators can detect defects (burs, scratches,
incomplete features etc.)
See also Measurement