After playing around with the machine more tonight, I've definitely noticed a correlation. The more you move the axis the more it is off. I've experimented in both + x and - x. Maybe the math is off somewhere or I am supplying the wrong information. . .

5mm pitch on the ball screws, evidence here (deluxe kit):

http://www.cncfusion.com/smallmill1.htmlI think the 200 steps/rev on the steppers is typical. I bought Nema 23's 370 from novakon.

Steppers are directly attached to the ball screws.

Gecko drives should be 10 microstepping.

25.4mm to an inch. I thought this was exact but maybe some units are left off?

I suppose I could try setting the mill up in mm and see how it reacts then. I can still use imperial from the DRO by switching the units with the gcode, right?