so , I am in the shop, and I am doing the following.
ref all home
I moved the head down, so as not to hit anything, then zero'ed everything
so from the controller:
i hold the Z- button, and the head travels down, and the DRO reads -8
i hold the Z+ button, and the head travels up, and the DRO reads +17 now
i hold the pg-down button, and the head travels down, and the DRO reads +7
i hold the pg-up button, and the head travels up, and the DRO reads +2 now