Trak DRO Calibration

Anyone know how to calibrate a Trak DRO?

It has these sensors that ride on the back of the bed for X and on a
bar mounted to the knee for Y. There's a wheel in there that is
slightly ridged to get a grip. The wheel has a radiused face like a
bike tire. There are asjusting screws on the mount to let you rocker
the wheel. My guess is that rockering it to 90 degrees gives you the
max wheel diameter and thus the least revs per inch. Rockering it to
the edge of the wheel gives you a smaller diameter and the most revs
per inch. 'Course this is a small variance.

The problem was that my parts were "growing". Two of them grew
exactly the same. So that was interesting. But growth would be bad.
These are parts for my X and Y CNC drives.

It also seems to know where "home" is, but I can't figure out how to
set home. Maybe home is set at power on.......

Thinking out loud I guess I need to check / clean all the contacts.
Noise from that could mess it up I 'spose.

Anyway, if you know anything about one of these I would appreciate
any help.

Thanks,
-jd