optical indicator

optical indicator

[′äp·tə·kəl ′in·də‚kād·ər] (engineering) An instrument which makes a plot of pressure in the cylinder of an engine as a function of piston (or volume) displacement, making use of magnification by optical systems and photographic recording; for example, the small motion of a pressure diaphragm may be transmitted to a mirror to deflect a beam of light.