Siemens SINUMERIK 840D sl Programming Manual page 377

Coupling factor
The coupling factor specifies the desired relationship between the paths of the coupled axis
and the leading axis.
Formula: Coupling factor = Path of coupled-motion axis/path of trailing axis
If a coupling factor is not programmed, then coupling factor 1 automatically applies.
The factor is entered as a fraction with decimal point (of type REAL). The input of a negative
value causes the master and coupled axes to traverse in opposition.
Acceleration and velocity
The acceleration and velocity limits of the combined axes are determined by the "weakest
axis" in the combined axis pair.
Status of coupling
You can query the status of the coupling in the NC program with the following system
variable:
$AA_COUP_ACT[axis]
0: No coupling active
8: Coupled motion active
Job planning
Programming Manual, 03/2006 Edition, 6FC5398-2BP10-1BA0
Path traversing behavior
9.2 Coupled motion (TRAILON, TRAILOF)
9-11