I have Datum Plane A and Point B. I output the location of both in the Y-axis (Result-A and Result-B), then output the distance between the two in the Y-axis (TOL/DISTB, NOMINL, 0.00,-0.05,0.05,YAXIS,AVG) as Result-C. It would seem that if I subtract Result-B from Result-A, I should get Result-C. However, Result-C as output as a distance by the program is not always the same as the simple subtraction result. For example: On one part, Result-A=144.020, Result-B=144.031, and Result-C=0.011. This is, as I feel, as it should be. However, the next part Result-A=144.047, Result-B=144.029, and Result-C=0.034! Subtracting Result-B from Result-A is only 0.018!! Why is there a difference? Both parts were measured with the same program, in the same fixture, one right after the other without moving or modifying the fixture.