Siemens SINUMERIK 840Di Function Manual page 751

Fig. 2-8
The zero of the coordinate system MCS corresponds to M and the zero of the WCS
corresponds to W. In the working space of the machine the reference point is defined as R
and the toolholder reference point with T.
2.2.2 Position of coordinate systems and reference points
Control POWER ON
For incremental measuring probes, the reference point must be approached each time the
control is activated so that the control can transfer all position values to the coordinate
system.
Axis Types, Coordinate Systems, Frames (K2)
Function Manual, 08/2005 Edition, 6FC5397-0BP10-0BA0
Zeros and reference points on a turning machine
Detailed Description
2.2 Zeros and reference points
2-21