| Once they work, then they work - if that makes sense. As long as you've got the sensor in a reasonably clear position, on the correct side of the bike - most circuits are on the right side - then it should be fine.
My sensitivity is set to 6 (middle I think) and as long as the delay is just under what your very fast lap time would be - you should be OK.
They either seem to work or not work at all !!! Or if they are showing too many laps, it might be that someone has position a beacon halfway round the track (hence the reason for correctly setting the delay).
If yours is working half the time, it maybe that the delay (the time that it will ignore signals) is set over a normal laptime
HTH
Tim | 
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