If a Precision Bar and Depth Gauge Are Being Used

If a precision bar and depth gauge are being used to measure the distance between the long legs of the center support and the low/reverse piston of a GM 6T40 transmission, what must be done to get a correct calculation?

A) The thickness of the precision gauge must be added to the measurement.
B) The thickness of the precision gauge must be subtracted from the measurement.
C) The depth of the low reverse steel and the step of the transmission case must added to the measurement.
D) The depth of the low reverse steel, as measured from the step in the transmission case, and the thickness of the precise measurement must be added together to obtain the specified measurement.