Siemens SINUMERIK 840DE Programming Manual page 241

Deactivate mirroring
For all axes: MIRROR (without axis parameter)
All frame components of the previously programmed frame are reset.
Note
The mirror command causes the control to automatically change the path compensation
commands (G41/G42 or G42/G41) according to the new machining direction.
The same applies to the direction of circle rotation (G2/G3 or G3/G2).
Fundamentals
Programming Manual, 10.2004 Edition, 6FC5 298-7AB00-0BP1
6.7 Programmable mirroring (MIRROR, AMIRROR)
Frames
6-33