optical reference plane
Technical term in computing and optics; a plane used as a reference for optical measurements or alignment.
Please set the optical reference plane before starting the measurement.
Compound of 光 (ひかり, 'light') + 基準 (きじゅん, 'standard') + 面 (めん, 'plane, surface'). The exact historical derivation is uncertain; the term is a modern technical coinage.