The optical reference profilometer is a coordinate measurement machine (CMM) configuration that utilizes a special optical referencing frame to provide a stable and accurate surface measurement. This referencing frame provides several mechanical advantages that make it possible to use lower precision mechanical components while still maintaining high measurement accuracy. The optical reference profilometer also provides reduced measurement sensitivity to thermal variations of the environment. By utilizing a superinvar metering rod network, this CMM system is essentially thermally insensitive to temperature changes of the order of 1°C. This special feature makes the optical reference profilometer functional at a high measurement accuracy level in an open laboratory environment. © 2001 Society of Photo-Optical Instrumentation Engineers.