A dial to see if the ball screw moves in and out is a good idea, and the first place to look. This would indicate bad bearings or perhaps a bearing locknut that has loosened up.
The nextplace to look would be the ball nut and its mounting to the table. Is there oil on the ballscrew?
When backlash is dialed in (you can watch one of the LEDs on the BMDC or go to the fist monitor and watch the Y axis. The first 2 characters are the backlash.) you need to reboot the machine. That is when the control looks at the pots and translates the resistance value to a backlash value.
George
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)