As far as the zero approach, the tolerance can not be higher than the setting. Set it to something like 1" for the X Axis to try it. Set tolerance to zero.
From the DRO Operation Screen: (Make sure you are in Inch Mode before doing anything below)
Press Right Arrow
Setup
User Setup, press SEL
Press Down Arrow and get to Zero App Tolerance, set that to 0.0000
Press down arrow to Select Axis
Select the axis you want to set the Zero App on (Say X Axis for this example)
Press the down arrow to Zero App Distance, set this to 1.0000
Press the down arrow until you are at Save & Exit
Press Save
Now press the Down Arrow until you see Save & Exit
Press Save
Now you are back at the home DRO Screen
Press Fn
Make sure Zero Approach is on. If not, then turn it on, and press Exit.
This is something you would use if you are milling or turning a long part and want it to beep when you get close. Like an inch away, maybe 5", depending how fast you are going.
Its more of a warning you set up. Example is to set it at 1" Above. Thats good for slow feed rates on a mill or lathe, you want more if its faster. Then you can turn the beep off and on as you please with just a couple buttons.