To compute the time for speed indexes above 100, subtract the time interval fro the appropriate distance once for each point above si-100.   Example: You want to compute the time for a 440 yard race where the winning horse's speed index was 106.   The time interval for 440 yards is .044.   So, multiply .044 by 6 which is .264; subtract .264 from the base time for si-100 (:22.050), and you arrive at the minimum time for your race, which is :21.786 (the maximum would be :21.743).

        Conversely, to compute the time for speed indexes below 100, add the time interval for the appropriate distance once for each point below si-100.   Example: You want to compute the time for a 440 yard race where the winning horse's speed index was 91.   You would multiply .044 by 9 (100 - 91 = 9), which is .396; add .396 to the base time for si-100 (:22.050), and you arrive at the minimum time for your race, which is :22.446 (the maximum would be :22.401).

        Times at one speed index do have room for variance - for example, a si-97 at 220 yards can be any time from :11.995 to :12.016.

        To determine speed indexes for non-winning horses in a race, first assign the speed index and time to the winning horse.   After that, use one of the two formulas, depending on the distance of the race:

            One-quarter length equals one SI point for all straightaway races up to and including 660 yards.
            One-half length equals one SI point for all around the turn races at 660/770/870 yards.

        If the winning horse in a straightaway race is half-a-length ahead of the second place horse, and the winning horse's speed index is 96, then the second place horse gets a speed index of 94.

        If the winning horse in an around the turn race is half-a-length ahead of the second place horse, and the winning horse's speed index is 96, then the second place horse gets a speed index of 95.

        AQHA Rule 301(a)(5): "In qualifying for a Speed Index Rating, standard weight shall be 120 pounds.   Should a horse carry less than this amount in a race, one-tenth of a second will be added to the official time for each four pounds or fraction thereof less than 120 pounds."   Example: A horse who won at 440 yards in :22.182, but who carried 116 pounds, would have one-tenth of a second (0.10) added to their time, which would result in a speed index of 94, instead of 97.   A horse who did not win, but who carried 116 pounds, would have to have his base speed index calculated based on the winner's speed index; look at the time for that SI on the chart, add 0.10 seconds, and assign the speed index corresponding to the adjusted time.

        A neck and 1/4-length are the same thing.   It is properly a neck, unless you're into measurements of over one length, such as 1-1/4 lengths (you'd write that as "1-1/4" not as "1 + nk").   Times faster than the real world record times must never be assigned.