Ran the numbers from the Fuji datasheet. Schwarzschild exponent calculates consistently to 0.5 at all the given data points.

To calculate an adjusted exposure time (not aperture adjustment) it's:

corrected exposure time in seconds = (t+1)^(1/p)-1

where t is the metered exposure time in seconds and p is the Schwarzschild exponent

Chart attached. Have fun.

Lee