For the series races, SPSA uses the “Time-on-Time” method prescribed by US Sailing. This method better compensates for large handicap spreads in PHRF sailing clubs and allows for adjusting the corrected time by a wind factor to give more time allowance for light days.

The formula for the “Time Correction Factor” is: TCF = A / (B + PHRF)

US Sailing suggests that A be set to 650, but notes that any value can be used. The Regatta-Tech software uses the same value for the A & B variables when making a wind adjustment.

The B variable is the wind correction factor. The use of this is subjective from club to club. Typically we use the following values to adjust for the various wind conditions:
480 – Heavy, 15kts +
550 – Average, 10-15kts
600 – Light, 5-10kts
650 – Calm, 1-5kts

The corrected time is then calculated by multiplying the elapsed time by the TCF.

So given a PHRF rating of 194, a light day, an elapsed time of 43:53 the corrected time would be calculated as follows by the Regatta Tech software:

600 / (600 + 194) = .7557
43:53 = 2633 seconds x .7557 = 1989.7 seconds == 33:09.7

For complete details, see: US Sailing Time-on-Time