Siemens SIMATIC S5 Manual page 151

IP 266
Result: The IP 266 chooses the preferred direction. Due to the programmed
backlash, the movement takes longer than it would in the opposite direction.
The distance for the motor-driven axis is longer by the backlash compensation
value.
The function selects the direction of travel only when absolute target posi-
tions have been defined.
G26: Approach target in a clockwise direction
All absolute target positions are approached in a clockwise direction.
G27: Approach target in a counter-clockwise direction
All absolute target positions are approached in a counter-clockwise direction.
G26 and G27 are effective only in conjunction with "Absolute size
specifications" (G90).
• G40: Disable tool offset
G43: Enable positive tool offset
G44: Enable negative tool offset
A tool offset can be regarded as a coordinate shift, and is required to
compensate for changes in the tool length caused by tool wear. An existing
traversing program need not be reprogrammed to include a tool offset, but is
adapted via a compensating factor.
Periodic tool wear (e. g. drill wear) can be measured and corrected using the
G functions. The following table shows the effect of a tool offset.
EWA 4NEB 812 6057-02
Machine Data, Modes and Traversing Programs
5-79