Transponder timing (also called chip timing or RFID timing) is a technique for measuring performance in sport events. A transponder working on a radio-frequency identification (RFID) basis is attached to the athlete and emits a unique code that is detected by radio receivers located at the strategic points in an event.

The most common transponders come in two types. One is worn on the shoe, one is worn on the race number. The first type, commonly called the "D" tag, is affixed to the race number for registration purposes and then removed by the participant prior to the event and looped through the shoe laces of one of his/her shoes. The actual transponder is located inside of the loop.

The second, commonly called the "B" tag, is affixed directly to the back of the race number prior to registration and is worn that way during the event.

Either type works well with Rainbow race numbers. For more information on chip timing technology and various suppliers click here.