What is a Tach?
A tach is short for the word tachometer, which is a combination of the Greek and Latin words for measure and speed. A tach is used to measure angular speed of something that is rotating. The most common kind measures revolutions per minute (RPM) of a crank shaft on the engine of an automobile, aircraft, tractor or truck. Many tachometers also have an hours meter that measures how many hours an engine has been run at a certain RPM. The hours measurement is primarily used for service intervals and is mostly seen on aircraft and tractors. For example, a tractor will need its oil changed every 30 hours or six months instead of a certain number of miles or kilometers. A tach usually displays RPM on a calibrated analog or digital display. The display on most tachometers indicates safe operation zones, with speeds past the maximum operating speed marked in red. Operating a vehicle or aircraft past the maximum operating speed (also called “redlining”) of these safe zones may cause excessive we
