Technology’s Touch: How a Photo Finish in the Olympic Pool Gets Resolved

Inside the timing suite for the Olympic swimming races. How accurate are those touch pads and clocks?

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Omega

The timekeeping room from the Aquatics Center in London

As dramatic as Olympic competition is, nothing beats a to-the-wire finish. Or what looks like a dead heat. And when that happens (remember Michael Phelps’ one-one hundredth of a second victory over Serbia’s Milorad Cavic in the Beijing Games, or Dara Torres’ loss in the 50m freestyle by the same amount?), you can’t rely on the human eye.

That’s where some serious computing power and intense time-keeping come in. As the official time keeper of the Games, Omega developed the touch pads in the pool and the sense pads on the starting blocks that are making their Olympic debut and can measure finishing times down to fractions of seconds. It’s not the technology that limits timing precision, it turns out, but other factors like engineering and the way pools are made that federations take into account when setting the threshold for ties.

Let’s start with the starting blocks. Omega officials gave reporters a behind-the-scenes look at the timing suite on the pool deck at the Aquatics Center where any razor-thin differences will have to resolved, on the spot, with the help  of redundant timing systems  and a lot of computers. New in London are wedges, similar to those that track athletes use, installed on top of the blocks to give swimmers more stability and momentum to launch themselves into the water. With the innovation, however, also comes more opportunity to objectively measure how athletes dive into the pool and to distinguish false starts, particularly during relays when swimmers cannot enter the water until their teammate touches the wall first, from legitimate ones. Working with biomechanical scientists, the timers calculated the start time, which is how long it takes for the human body to push itself against the block and propel horizontally forward, or how long it takes from that push-back moment to the time it takes for the foot to peel itself completely off the blocks (which is about 27/1000 of a second). Based on that, they figured out that in a relay exchange, any start time registered by a waiting swimmer on the blocks that is less than 0.04 seconds after his teammate in the water touches the wall is a false start.

While all this technology can break down the seemingly intuitive performance of athletes into hard numbers, there are limits to the power of statistics. The clocks, for example, can technically slice time down to one-one millionth of a second, but many sports federations, including swimming’s FINA, consider one-one hundredth of a second a tie. Why? Because at that level of precision, you have to be certain that the pool is built exactly symmetrically so that every lane is the exact same length down to fractions of millimeters. And even at one one-thousandth of a second, there can be no more than 1.7mm leeway difference in length — and pools are typically built to specifications that are within centimeters. Other sports allow greater precision — in sliding events and track cycling, for example, athletes are timed down to the thousandth of a second. But in a pool, “how can you guarantee that each lane is measured precisely to fractions of a millimeter?” says Peter Heurzeler, the past president of Omega Timing who recently retired after clocking athletes at world championships and Olympics since 1969.

If Phelps has another close race to the wall, 15 people in that timing suite on the pool deck will be ready to run the numbers. To make doubly sure that even wisps of seconds aren’t lost, a camera system attached to its own timer provides another, bird’s eye of the finish. That’s how Phelps’ win in the 100 butterfly in Beijing was determined. The camera’s shutter clicks 100 images per second, and by comparing Phelps at the wall to Cavic, officials could see that Phelps finished first — by one image.

And how sensitive are the touch pads installed in each lane? Fingers have to register at least 1.5 kg of force to be a legitimate touch; a wave caused by swimmers moving through the water or pulling away during a turn can generate about 1kg of force, so a hand has to push slightly harder than that to record a touch.

Which means that in the Aquatics Center in London, coming to the wall doesn’t just mean putting your hand on the touch pad first. It means pushing it — by 2 mm — as well. Who knew there was so much in a touch?

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