Siemens SINUMERIK 828D Programming Manual page 14

Fundamental Geometrical Principles
1.1 Workpiece positions
Figure 1-2
The workpiece zero (W) is the origin of the workpiece coordinate system.
Sometimes it is advisable or even necessary to work with negative position specifications.
For this reason, positions that are to the left of the zero point are assigned a negative sign
("-").
14
Workpiece coordinate system for turning
Programming Manual, 07/2010, 6FC5398-1BP40-0BA0
Fundamentals