dont know for sure but when two lads in my club brought there clocks in for 1st race last year to be set,they where both flashing.they where both used all season with no problems.1 lad got new battery fitted for this year,other one never bothered, 1st race this year brought clock back still flashing ,he used it for 1st race when i got it out of cupboard to set it for next race it had stopped flashing,WHY i dont know