I have created a slightly custom screen for my machine. Mostly, I have deleted all things related to the 'Y' axis since the machine doesn't have one. Our machine is X, Z, A, B for several reasons.
Anyway, the 'Zero Z' button does not change the DRO, or seem to have any effect. It is configured in the screen editor the same as the 'Zero X' (which does work) except for: position, label and Name: btnZeroZ

Any suggestions on where to look for the difference and how to change it to make it work?

Verify that it says Zero Z next to Left Up Action.

Thanks for the suggestion. I’ve been traveling and was just able to try this. This was not the issue but gave me another place to look.

Turns out that the problem was the dro was configured for machine coordinates rather than multiple coordinates.

Thank you Bill_O