Fully automatic timing

Fully automatic time (abbreviated FAT) is a form of race timing in which the clock is automatically activated by the starting device, and the finish time is either automatically recorded, or timed by analysis of a photo finish. The system is commonly used in track and field as well as horse racing, dog racing, bicycle racing, rowing and auto racing. In these fields a photo finish is used. It is also used in competitive swimming, for which the swimmers themselves record a finish time by touching a touchpad at the end of a race. In order to verify the equipment, or in case of failure, a backup system (typically manual) is usually used in addition to FAT.

In races started by a starting gun, a sensor is typically attached to the gun which sends an electronic signal to the timing system when fired. An alternative starting light or sound which is electronically triggered, such as a horn, is typically also wired to the timing system. In sports that involve a finish line that is crossed (rather than a touch finish, as in swimming), the current finishing system is a photo finish which is then analysed by judges.

The current photo-finish system used in Olympic competition, as well as other top-level events uses a digital line-scan camera aimed straight along the finish line. TimeTronics, FinishLynx and Omega are examples of commercial timing systems commonly used in athletic competitions. These cameras have an image field only a few pixels wide, with a single frame forming a narrow image only of the finish line, and anything which is crossing it. During a race, the camera takes images at an extremely high frame rate (the exact rate depends on the system, but can be in the thousands of lines per second). Computer software then arranges these frames horizontally to form a panoramic image which effectively displays a graph of the finish line (and anything crossing it) as time passes, with time denoted on the horizontal axis.

...
Wikipedia