A tachymeter is a device that measures speed by determining how long it takes to cover a given unit of distance like a mile or a kilometer. By measuring travel time, the device can extrapolate to determine overall speed. The precision can vary, depending on the application and the device, and there are a number of products on the market that offer this functionality.
One of the most famous examples of a tachymeter is as an extra feature on a watch. Some watches, usually luxury products, have a tachymeter bezel, with increments marked out to assist with making such measurements. The user can start and stop a timer to measure travel time. For example, a horse trainer at the track might start the tachymeter when a horse moves over the starting line, and stop it at the first furlong post. The device will provide information about how many furlongs per hour the horse can cover.
Such tools can be useful for some kinds of scientific measurement, as well as travel planning and racing. Athletes, jockeys, and race car drivers may use a tachymeter in training to track speed and develop a training routine. The devices can also be used by trainers and enthusiasts to monitor performance. This may help with decisions like a training schedule or which horse to bet on in the afternoon races.
Tachymeter watches need to be carefully calibrated to provide accurate readings. If the watch is off, the measurements will not be accurate. Watch manufacturers and repairers can check watches to confirm that they are working properly, and may service them if necessary to get them back on track. Some manufacturers provide this as a free service to back the watch warranty, on the grounds that their products should function well for the lifetime of the warranty. If a serious product flaw develops, the manufacturer may replace the whole watch.
When using a tachymeter, it is important to pay attention to the units of measurement being used and to calculate information accurately. If the tachymeter provides a reading in meters, for example, it needs to be converted to express the speed in kilometers per hour. Some devices will do this automatically and may also store information and statistics for the operator. Scientific instruments with this functionality can also communicate with a base unit or laptop to provide continuous information in a format that can be stored for future reference and review.