Siemens SINUMERIK 840D sl Programming Manual page 279

Plane definition
The measuring cycles work internally with the abscissa and ordinate of the current plane
G17 to G19.
The default setting for turning machines is G18.
Note
Spindle
Spindle commands in the measuring cycles always refer to the active master spindle of the
control.
When using measuring cycles on machines with several spindles, the spindle concerned
before the cycle call must be defined as the master spindle.
References: /PG/ "Programming Guide: Fundamentals"
Measuring cycles
Programming Manual, Release 04/2006, 6FC5398-4BP10-0BA0
Measuring Cycles for Turning Machines
6.1 General prerequisites
6-3