Good day again Almost there

Sorry posted to soon do not now how to remove

I am having problems with the z offset

I set it to the block gauge height +.125 (am in inches)
Select tool turn on feature and it read 1.128 ( discover that in line g54 it had that as a preset offset so I reset to zero)
rebooted software g54 now has no offset at z
selected tool and turned on z offset it now says  -.120 less than set and neg ?

Now really lost do I set z to top of work and zero or to  +.125 and zero or neither and don't zero?

I have tried most of those ways an broken several tool bits as expected.

Any help greatly appreciated and believe me needed

Henry