Hi,
not sure I can help but maybe...
The units you set in the 'native units' are critical because they are used in your motor tuning.
Native units should be set when you set up your machine then not touched.
What units do you use to tune your motors? Do you calculate the steps per unit or do a 'measure
and see' approach.
While I calculated my steps per unit and I believe is preferred because of its accuracy a lot
of users are confused by the calculation and prefer the measure and see approach.
Do yourself a favour and use the units determined by the machine, usually the ballscrews.
If the pitch of the screws is 5mm then use metric for your native units or if the pitch is
1/4inch then use inch. At runtime you can set the display units to whatever you're most
comfortable with.
Once you've set the steps/unit values and motor tuning then worry about the DRO's.
Your post said you used M20, that is not correct, it should be G20.
Craig