Where #Lg = the base longitude, and #Lt = the base latitude,
and where Lg is your local station longitude and Lt is your local station latitude,
And where #Lg, Lg, #Lt, and Lt are in decimal degrees, the corrected time (in minutes) is derived as such:
You need also to pay attention to the value sign of the number. The longitudes and latitudes must be expressed with the correct sign. Longitudes are measured positive to the East, and Latitudes are measured positive to the North. Note that longitudes in North America have a negative value. As a simple rule of thumb:
On 22 Jun 2013 at 3h 10m 54s, SAO18479 will be occulted by the moon for Bonner Springs KS, located at: W -94d 53m 35.5s, N 39d 3m 28.6s
The given A/B factor by the Occult Software shows A = +1.9, B = +1.2
Find the predicted time for a site located in Blue Springs MO, located at: W -94d 20m 42.4s, N 39d 1m 40.2s
Convert the Base Station coordinates to decimal degrees: #Lg = -94.8932 and #Lt = 39.0579
Convert the Local Site Location coordinates to decimal degrees: Lg = -94.3451 and Lt = 39.0278
Solve for the unknowns in (A * (Lg-#Lg)) + (B * (Lt-#Lt))
A * (Lg - #Lg) = 1.9 * (-94.3451) - (-94.8932) = 1.0412 [Lg-#Lg = Positive which shows local station longitude is EAST of Base]
B * (Lt - #Lt) = 1.2 * (39.0278) - (39.0579) = -.03613 [Lt -#Lt = Negative which shows local station latitude is SOUTH of Base]
Add the two quantites together:
1.0412 + -.03613 = 1.00507m = 1m .3s later than Base Station Time
Base Station Time of 3h 10m 54s + 1m .3s = Local Station Time = 3h 11m 54.3s
Using Occult Software, and running predictions for the Blue Springs site, the Local Station Time shows: 3h 11m 51s for time of disappearance.
The difference of 3 secs between the time using the A/B factors and a direct computation is quite good.
It can be significantly larger due to differences in the limb. And the difference gets larger as the distance increases.
For those wishing to obtain more accurate predictions, it is suggested downloading and installing the Occultation of Occult Software, authored by David Herald.