Good question,
The FEI rulebook, nor the new "timing" guidelines give no definitive answer in relation to the height of photocells. The only clue that we get comes from the new "timing" rules as listed here:
2.3.1 Timing at the sensors
With electronic timing, the time is taken when a horse crosses the start or finish line
and triggers the beam between the photocells. Time has to be taken on the breast
of the horse. If the rider pushes the horse’s head first there will be no correction.
With hand timing the time will be taken as above. The height of the sensors must be
identical at the start and finish lines.
Based on a meeting of officials out on the jumping course of the Adelaide CCI**** competition one year, it was decided that the optimum height to set the photocells to was 1.10 metres, in order to obtain the horse's
breast, as listed above. I have used that height since.
My view is to not get too hung up on the height, to the millimetre. What is more important is to ensure that the photocell height for the start is the same as for the finish, in order to compare like for like. I was glad that the "timing" committee adopted this rule following the public comment period.
I believe that the FEI Timing Booklet is due to be published, which I hope will contain an answer to this, amongst other things. In the meantime I hope that this explanation will help you answer your question.
Regards,
George.
