506x are the user coordinates. I'm not sure whether these relate to G54 or whether the current fixture offset is used - I have only tested with G54.

507x are the machine coordinates. I agree that the probing module is confusing.

Allan

Alan, makes sense to me.  I still have not been able to test a good fixture offset.

The term absolute is used because the positions in those variables are always absolute.  G53 is always absolute.  However, work offset coordinates (G54-G59, etc..) can be called out as incremental or absolute depending on G90/G91.  What they are trying to convey is that no matter if you are probing in G91 mode, those variables will always be the absolute positions. 

For example.
G90 G00 X1
G91 G31 X1 F10

Say the probe struck at X==1.5.  The value in 5061 will be 1.5 and not 0.5. 

Steve

Steve, I see where you're coming from. . Thanks for that clarification.

Allan