Siemens SINUMERIK 840Di sl Programming Manual page 344

Tool offsets
8.8 Tool radius compensation (G40, G41, G42)
You can generate equidistant paths with OFFN, e.g., for rough-finishing.
Programming
G40
Or
G41
Or
G42
or
OFFN=
Parameters
G40
G41
G42
OFFN=
344
Deactivate tool radius compensation.
Activate tool radius compensation; tool operates in machining
direction to the left of the contour.
Activate tool radius compensation, tool operates in machining
direction to the right of the contour.
Allowance on the programmed contour (normal contour offset).
Programming Manual, 11/2006, 6FC5398-1BP10-2BA0
Fundamentals