Siemens SINUMERIK 808D ADVANCED Programming And Operating Manual page 18

Relative coordinate system (REL)
In addition to the machine and workpiece coordinate systems, the control system provides a relative coordinate system. This
coordinate system is used to set reference points that can be freely selected and have no influence on the active workpiece
coordinate system. All axis movements are displayed relative to these references.
Clamping the workpiece
For machining, the workpiece is clamped on the machine. The workpiece must be aligned such that the axes of the
workpiece coordinate system run in parallel with those of the machine. Any resulting offset of the machine zero with
reference to the workpiece zero is determined along the X, Y and Z axis and entered in a data area intended for the settable
work offset. In the NC program, this offset is activated during program execution, for example, using a programmed G54
command.
The figure below shows an example of the workpiece clamped on the machine.
Current workpiece coordinate system
The programmed work offset TRANS (Page 56) can be used to generate an offset with reference to the workpiece
coordinate system, resulting in the current workpiece coordinate system.
Programming and Operating Manual (Milling)
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6FC5398-4DP10-0BA1, 01/2014