beam of light from a light source is reflected by a polyhedral mirror which is continuously rotating in a constant speed around its axis, and the reflected beam sweeps on an object and passes a predetermined point of the object surface, mõõtevahend, milles valgusvihk valgusallikast peegeldub peegli poolt, mis pöörleb pidevalt konstantse kiirusega ümber oma telje, ning peegeldunud kiir kompab objekti ja läbib objekti pinna etteantud punkti