The coloured segments are to help time the start of a race. At 10 minutes to go, five minutes and the actual start a gun is fired. The tactic is to cross the start line at full speed as soon as possible (like a second or two) after the start gun. Crossing even one second before means that the competitor has to do a 360 around one of the end points of the start line and so will lose possibly minutes. It's the navigator's job to inform the helm (person steering) how long there is to go, it's the helm's job to get the speed and crossing time right..
Of course any chronograph will time 10 minutes accurately, I used my Carrera with no coloured segments for the job when I was racing yachts.
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