Close finishes are settled by an image that looks like a photograph but is not one. Understanding how it is produced explains why the resulting decision can be trusted to a very small margin.
The camera records a line, not a scene
A finish camera is aimed precisely along the finish line and captures only a single vertical strip of the world, thousands of times each second.
Those strips are placed side by side to build an image, so the horizontal axis represents elapsed time rather than distance across the track.
A competitor moving quickly therefore appears narrow and a slower one appears stretched, which is why athletes in the image look distorted.
Alignment is the critical setup task
Because the camera only sees the plane of the finish line, any misalignment means it is recording a slightly different position from the official one.
Installation involves aligning the camera to the line and verifying it against fixed markers before competition begins.
The system is also synchronised with the starting device, so the time axis of the image begins at the exact instant of the start signal.
The torso determines the result
In running events the finish is judged by the torso rather than the head, an arm or a leg, which removes an easy way to gain a false advantage.
Judges therefore identify the leading edge of each athlete's torso in the image and read the time at that horizontal position.
Other sports define the finishing point differently, so the same technology is read against a different body reference depending on the discipline.
Published times are rounded upward
Timing is captured more finely than the published result, and times are rounded up to the published precision rather than to the nearest value.
This ensures a published time is never faster than the performance actually recorded, which matters for record ratification.
Two athletes may consequently share an identical published time while the image places one clearly ahead, and the placing rather than the time stands.
Touchpads and transponders solve different problems
Swimming uses pressure-sensitive pads at the wall, because a camera cannot reliably see a swimmer's hand arriving beneath the water surface.
Long-distance road events use transponders, since a field of thousands cannot be resolved individually in a single image at the line.
Each method is chosen because of what the finish physically looks like, which is why timing technology is not uniform across the programme.
