tachymetr

A tachymeter is a specialized gauge found on analog speedometers in vehicles, particularly in automobiles, motorcycles, and some aircraft. Its primary function is to estimate travel distance based on the vehicle's speed and the elapsed time. The tachymeter operates by converting the speed reading (typically in kilometers per hour or miles per hour) into an approximate distance traveled over a set period, often one hour.

The scale of a tachymeter is usually positioned on the outer edge of the speedometer dial, marked in increments corresponding to distance (e.g., kilometers or miles). To use it, the driver notes the speed at the start of a journey and then reads the distance traveled by locating where the speed needle intersects the tachymeter scale after a given time. For example, if the speed is 60 km/h and the needle aligns with the "60" mark on the tachymeter after one hour, it suggests the vehicle has traveled approximately 60 kilometers.

Tachymeters were particularly common in older vehicles before the widespread adoption of digital odometers and trip meters. While modern cars often rely on electronic distance tracking, tachymeters remain a nostalgic feature in vintage and classic automobiles. They are also found in some aviation instruments, where they assist pilots in estimating flight distance based on airspeed.

The accuracy of a tachymeter depends on maintaining a constant speed, as any variation in speed can lead to discrepancies in distance estimation. Despite their simplicity, tachymeters provide a quick and convenient way to approximate travel distance without requiring additional instrumentation.