I dont know what is so hard about this. If the horse is running a 24 sec quarter, it's 7 len. per sec. If a 25 sec. quarter it's about 6 1/2 and a 26 sec quarter about 6 len. Going from memory but I think that's right.

If the horse you're trying to measure is moving much faster than the horse with the known time, then you can adjust it. Like the horse with the know time runs a 25 sec quarter, but your horse made up 5 len, then okay assume he is running a bit faster at: 7 lenghts per sec. Difference is only 0.14 vs 0.15 of a sec/length.

Like ateams example. SInce he made up 5 lengths on the 6 1/2 length/sec horse, just assume he's moving 7 lengths per sec. He made up 5 lengths, multiply by 0.14 and therefore he ran 0.7 sec. faster.

Possible error of .05 sec. doing it the other way? How accurate can you get?