When measuring injector components for diesel engines, for example, diameter tolerances of better than 5µm are required. To measure these tolerances reliably (measurement process capability), it is necessary to ensure measurement errors less than 0.5 µm. One prerequisite for achieving this goal is that the measurement results be sufficiently reproducible.  An example is the measurement of diameter deviations of an injector nozzle spray holes (nominal value about 180µm).

Seen in image above: Diesel injector: a) Color coded plot of the form deviation of the spray holes b) Cross sections for measuring the diameter of a spray hole.