Siemens SINUMERIK 840D sl Programming Manual page 240

Measuring Cycles for Milling and Machining Centers
5.7 CYCLE998 workpiece: Angle measurement and ZO determination
2. With the spindle position that applied at the beginning of the cycle.
The tool radius of the probe + R or - R is defined as the trigger point defined for the axis
direction.
A multidirectional probe does not have to be calibrated at the beginning of the cycle for
measuring variant _MVAR=1105.
This measuring variant with differential measurement is only useful with the measuring axes
_MA=x01 or _MA=x02.
Notice
In the case of great measurement accuracy demands, differential measurement is not
recommended!
5-106
Programming Manual, Release 04/2006, 6FC5398-4BP10-0BA0
Measuring cycles