Siemens Sinumerik 840D sl Programming Manual page 255

Change in the working plane
The working plane (G17/G18/G19) cannot be changed if G41/G42 is active.
Change in tool offset data set (D...)
The tool offset data set can be changed in compensation mode.
A modified tool radius is active with effect from the block in which the new D number is
programmed.
Note
The radius change or compensation movement is performed across the entire block and only
reaches the new equidistance at the programmed end point.
In the case of linear movements, the tool travels along an inclined path between the starting
point and end point:
Fundamentals
Programming Manual, 01/2015, 6FC5398-1BP40-5BA2
11.1 Tool radius compensation (G40, G41, G42, OFFN)
G41
G42
Tool radius compensation
255