Basics of Coordinate Metrology
Unit 7: Structure of Coordinate Measuring Machines - Length Measuring Machines

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The points in a mostly Cartesian coordinate system probed by the stylus system are determined by the length measuring systems in each axis of the coordinate measuring machine. The length measuring systems consist of the measurement scales and the scale readers.

Opto-electronic incremental length measuring system with glass graduated
scale working by the transmitted light method (Source: Heidenhain, 1998)

 The systems usually used are incremental measuring systems, in which the measurement standard used are toothed racks, precision threaded spindles, graduated scales, Inductosyn scales and optic length standards (laser interferometers). The most frequently used systems are optic length measuring systems equipped with graduated scales. They work by the incident light or transmitted light method.

The length measuring systems are essential components for the precision of the coordinate measuring machine, which is why their resolution is at least one order of magnitude more precise than the length measuring uncertainty of the coordinate measuring machine.