I understand the concept behind compensated Rxs, but I don't understand how the computer comes up with the Rx. On the Varilux W2+ and the W3+, vertex is not taken into consideration, so why would the power change at the optical center? Why does one axis change by 1 degree, but the other changes by 18 degrees? Recent example:

Prescribed Rx

-8.75 -1.00 x 30
-9.50 -.50 x 10
+2.50 add

Compensated Rx
-8.39 -1.39 x 31
-9.25 -0.72 x 173
OD add +2.57
OS add +2.56