jeff 1/21/2016 1:01:00 PM  V1 is simply velocity in feet per second  first fraction most recent start  or velocity in feet per second  first fraction 2nd start back  whichever is higher.
Example taken from today's races:
Jan 21 2015 OPX R2 #8 HOT SHOES...
In her most recent start she was 3 lengths behind at the first fraction pace call in a 5f dirt race at DED. Distance of the first fraction was 2f or 1320 feet and the leader at the pace call was timed in 22.79 seconds.
I'm well aware an argument can be made that some other number is a better representation of 1 length  but assuming each length is worth 0.20 seconds  first fraction time for the example horse HOT SHOES in her most recent start was 22.79 plus 0.60 (or 3 times 0.20) seconds or 23.39 seconds.
Based on that, V1 for HOT SHOES can be calculated as follows:
V1 = 1320 / 23.39
or
V1 = 56.43 ft. per sec.
jp
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