I have a classic C-Beam XL build. It has Tr8*8-2p lead screw and given the micro stepping and steps per rotation of the motor, in theory I have have a steps / mm of exactly 200. However, it is actually much closer to 198.23. I can't figure out why it would be off by nearly 1%. What do other people have ? It is not backlash in that I measure this over a large distance and the backlash is less than .2 mm. I don't think I am loosing steps or anything - if I do lots of short moves in one direction then a large cumulative move back, I get to the same spot. If I move to the same location many times it is exactly repeatable. All my cuts are coming out well and seem the right size - I'm just really confused on why I would have this 1% error. When I look at specs on ACME lead screws, I don't know exactly what i have other than they came from open builds but it does not seem like any of them should have this much lead error. Few more details I'm using the DQ542MA Stepper Motor Driver stepper motor driver. Stepper motors are NEMA 23 Stepper Motor - High Torque Series and driving it from Arduino running a not too old version GRBL. Thanks for help.