Sport by Sport: Summer Games

Track
In sprint races like the 100-meter dash, which can last as few as 10 seconds, timing is of the essence. Therefore, every aspect of timekeeping is electronic, even the starting gun.

Once the runners are crouched with both feet on the pads on their starting blocks, a timing official pulls the gun's trigger, sending an electrical current through the attached copper wire cable to the starting blocks and a separate timing console. The current sets off a quartz oscillator in the timing console, while the sound of the gun is simultaneously amplified through speakers on each runner's starting block (so all competitors hear it at the same time).

At the other end of the race, a laser is projected from one end of the finish line to the other, where a light sensor, also known as a photoelectric cell or electric eye, receives the beam. As a runner crosses the line, the beam is blocked, and the electric eye sends a signal to the timing console to record the runner's time.

Photo courtesy Omega

Photo courtesy Omega

Meanwhile, a high-speed digital video camera aligned with the finish line scans an image through a thin slit up to 2,000 times a second. When the leading edge of each runner's torso crosses the line, the camera sends an electric signal to the timing console to record the time. The timing console sends the times to the judges' consoles and an electronic scoreboard. The images themselves are sent to a computer, which synchronizes them with the time clock and lays them side-by-side on a horizontal time scale, forming a complete image. The computer also draws a vertical cursor down the leading edge of each runner's torso at the time the finish line was crossed.

This composite image can then be broadcast on a video display within 30 seconds of the race's end to help make a decision on a close finish.

Photo courtesy Omega

In longer races, such as the marathon, the clock is still started with an electric gun. However, the large number of competitors makes it impossible for all the runners to leave the starting line simultaneously, and dozens of runners can cross the finish line at a time. Because of these considerations, marathons require a more individual system of timing -- radio-frequency tags (RFIDs).

Small RFID transponders are attached to each runner's shoe, sending out a unique radio frequency. Have you ever noticed the mat that stretches over the starting line at a marathon? It contains loops of copper wire than function as an antenna, picking up each runner's signal and sending the identification code and start time to the timing console. Mats are placed at 5-kilometer intervals to track each runner's progress, automatically displaying the best times on the scoreboard. Another mat is placed at the finish line to record each runner's finish time. Each competitor's time is then compared with the time clock, which was initiated by the starting gun and stopped running when the first runner crossed the finish line.

This technology is also used at the Boston, New York City and Los Angeles marathons, provided by companies such as Texas Instruments.

Cycling
Because cycling events face timing challenges similar to that of marathons, the technology is much the same.

Photo courtesy Athens News Agency

A radio transponder, attached to each bicycle behind the leading edge of the front tire, emits an identification code to antennas placed at the starting line, finish line and along the road. These antennas register each rider's time and send it to the timing console for comparison. Up to three high-speed photo-finish cameras are set up at the finish line, including above the track, to provide a time-sequenced visual record of the winners, including a vertical cursor delineating the front edge of each rider's tire, to be used in case of a close finish.

This technology is also used at cycling events such as the Tour de France, provided by Matsport out of Grenoble, France.

Aquatics
Similar to the short-distance track events, each swimmer's starting block has an attached speaker to announce the activation of the clock by the timing official, or starter. In an event like the relay, the swimmer in the water must "tag" the next teammate by pressing on a touch plate located on the pool wall. The contact plates -- made of thin stacks of PVC and horizontal strips that register focused pressure (as from a swimmer's hand) but not dispersed pressure (as from waves in the pool) -- then send a signal to the timing computer to record the first swimmer's time, denote the start of the second swimmer's time and report the time to the scoreboard.

Photo courtesy Omega Clockwise from top-left: Starting blocks; speaker; starting block and touch pad

The process works the same for the individual events such as breaststroke, freestyle and backstroke, during which the swimmer registers his or her time by pressing on the contact plate at the end of the run. Aquatics also use photo-finish technology similar to track events, recording an image of the finish at 100 frames per second.

Photo courtesy Athens News Agency