Definition
A handheld instrument that measures the rotational speed of a shaft, propeller, or other rotating part by aiming a focused laser beam at a reflective mark on the rotating surface and counting the number of times that mark passes per minute. The result is displayed in revolutions per minute (RPM).
Plain English
A small tool that measures how fast something is spinning by bouncing a laser off a reflective sticker on the part. Each time the sticker passes the laser, the tool counts it, and from that it works out the RPM.
Context Anchor
Seen in aircraft maintenance when checking the speed of an engine, propeller, rotor, fan, shaft, or other rotating part.
Derivation
Tachometer comes from the Greek tachos meaning 'speed' and metron meaning 'measure' — literally a 'speed measurer.' Adding 'laser' tells you how the speed is sensed: by a beam of light rather than by mechanical contact.
Why Pilots Care
Delivers accurate RPM data without attaching anything to moving components, reducing risk and setup time during engine testing.
Analogy
It is like counting how many times a marked bicycle wheel passes a flashlight beam, except the laser tachometer does the counting very quickly and displays the speed for you.
Intuition Check
A laser tachometer is not a cockpit tachometer display. It is a measuring tool used from outside the rotating part, usually during maintenance or testing.
Example Sentence 1
After replacing the tachometer in the cockpit, the technician used a laser tachometer to confirm the engine was actually turning at the indicated RPM.
Example Sentence 2
During a full-power run-up the laser tachometer gave steady readings that matched the cockpit tachometer.