A profile projector (also called an optical comparator) projects a magnified silhouette of a workpiece onto a screen for comparison against a template — it is explicitly named in this heading. Vision measurement systems that use digital cameras and software to perform dimensional analysis may also fall here if their primary function is dimensional checking, but systems with significant image-processing or machine-vision capabilities may be classified differently. The primary function test and the degree of optical versus computational measurement are the key classification factors.

Most aerospace and automotive quality systems require imported metrology equipment to arrive with a calibration certificate traceable to national standards (NIST in the US, or an equivalent national metrology institute in the country of manufacture). ISO/IEC 17025-accredited calibration is increasingly specified in supplier quality agreements. Importers should confirm calibration traceability requirements with the end-user before shipment, as retrofitting calibration after arrival can be costly and may not satisfy contractual requirements.