Siemens SINUMERIK 840D sl Function Manual page 145

Response of the AXIS-VAR server to errors
If the server cannot supply any values for an axis (e.g. because the axis concerned is a link
axis), then it returns a default value (generally 0).
For the purposes of testing, the machine data of the axis data servers below can be set to
sensitive, with the result that it returns an error message instead of default values:
MD11398 AXIS_VAR_SERVER_SENSITIVE
0: Default value
1: Error message
Extended Functions
Function Manual, 01/2008, 6FC5397-1BP10-3BA0
Several Operator Panels on Several NCUs, Distributed Systems (B3)
2.6 Link axes
145