Siemens SINUMERIK 840D sl Function Manual page 361

Positive backlash
The encoder leads the machine part (e.g. table). Since the actual position acquired by the
encoder also leads the real actual position of the table, the table travels too short a distance
(see diagram below). The backlash compensation value must be entered as a positive value
here (= normal case).
Figure 5-5
Negative backlash
The encoder lags behind the machine part (e.g. table). The table travels too far (see diagram
below). The correction value entered is negative.
Figure 5-6
Extended Functions
Function Manual, 03/2009, 6FC5397-1BP10-4BA0
Positive backlash (normal case)
Negative backlash
Compensations (K3)
Backlash compensation
361