X-Trial Starting The Countdown Clock

[doxiedad]

In X-Trial the course clerk stands at the start of the section, gives the rider the OK to begin, and then walks away. But the countdown clock doesn't start until the bike has moved past the base of the first challenge. A manual stop watch would be too subjective and inaccurate. Is there a hidden electronic device or photo eye?  

[trapezeartist]

I have always assumed it's manual. And they seem to give the rider a small amount of margin.