Siemens SINUMERIK 840D sl Programming Manual page 367

Further information
MIRROR X... Y... Z...
The mirror is programmed by means of an axial change of direction in the selected working
plane.
Example: Working plane G17 X/Y
The mirror (on the Y axis) requires a direction change in X and, accordingly, is programmed
with MIRROR X0. The contour is then mirrored on the opposite side of the mirror axis Y.
Mirroring is implemented in relation to the currently valid coordinate system set with G54 to
G57, G505 to G599.
CAUTION
The MIRROR command resets all frame components of the previously activated
programmable frame.
AMIRROR X... Y... Z...
A mirror image, which is to be added to an existing transformation, is programmed with
AMIRROR. The currently set or last programmed coordinate system is used as the reference.
Fundamentals
Programming Manual, 09/2011, 6FC5398-1BP40-2BA0
Coordinate transformations (frames)
12.7 Programmable mirroring (MIRROR, AMIRROR)
367