Originally Posted by

**jwatte**
Those numbers are where the spindle was located when you zeroed the axes. E g, "zeroing an axis" really means "put the negative value of the absolute position of the spindle, into the work coordinate system offset."

So, if the absolute value is X=2.5, Y=-1, Z=6, and you "zero axis" on all three axes, the G54 coordinate system will be X=-2.5, Y=1, Z=-6.

The DRO values you see for where the spindle is, are calculated as "the absolute position of the spindle (relative to the home of each axis) PLUS the current work coordinate system offset."

So, absolution position X=2.5, plus G54 offset X=-2.5, means that the DRO reads 0.

(Actually, hmm, I'm not at the machine right now, and I'm not sure if the absolute position is copied into G54 and the G54 offset subtracted; or whether the negative of the absolute position is copied into G54 and the G54 offset added -- it's the same result in the end, but if you edit G54 directly, obviously the sign matters :-)