Tacho

Tacho is a colloquial term used in several languages to refer to instrumentation related to measuring speed or rotational speed. In everyday use it most often denotes either a tachometer, which measures engine speed, or a tachograph, which records vehicle speed and driving times.

A tachometer, or tacho, is an instrument that displays the rotational speed of a shaft, typically the engine crankshaft, in revolutions per minute (RPM). It helps drivers gauge engine performance and shift points. In passenger cars it is usually a dial on the dashboard; in industrial settings it may monitor motors and turbines. Variants include analog gauges and electronic digital readouts.

A tachograph is a device installed in commercial vehicles to log operational data such as vehicle speed, distance traveled, and drivers’ working hours. Traditionally it recorded on a mechanical chart; modern systems are digital and store data in onboard recorders. Tachographs are used to enforce regulations on drivers’ hours and rest periods in many regions, notably the European Union, under rules such as Regulation 561/2006. Data can be inspected by enforcement authorities and, in digital systems, downloaded via authorized software.

In German-speaking countries, tacho is commonly used for both tachometer and tachograph, and the term is widely understood in other parts of Europe as shorthand for these instruments. In English, tachometer (RPM gauge) and tachograph (driving-time recorder) are distinct terms; “tacho” is less formal and more common in industry jargon.

See also: RPM, speedometer, vehicle safety regulations.