Idly searching for info on the C3 DRO (to get ideas for my own) I cam across the arceurotrade site where, against the C3 DRO info it states:

"
Note:
Depending on the actual lathe, you may experience some mechanical backlash. This can be removed by adjusting (machining or shimming) the collar under the handle.
If you find the instructions in the manual are limited, you may wish to refer to the following web link for more comprehensive details: http://www.mini-lathe.com/Minilathe/Reviews/SiegDRO/dro2.htm
"