In running races, the winner is the athlete whose torso crosses the line first. Hands, knees and heads don鈥檛 count. How, then, does the device that records the winning times work? In particular, how does it know which part of the body has crossed the line first? And how does it distinguish between all the athletes, some of whom must be obscured from a beam across the finishing line by their rivals?
Denholm Pickering, Birmingham, UK