I am working on my rebuilt cnc mill, how can i calculate the setting for motor tuning.

the stepper motor has a gear 18:30 I don't know the thread of the spindle on the X axis.
We did some test runs and came on a figure of 1375 for 75mm I can't explane this outcome I missing 0.10mm with this out come

Is there anyone how can help me to get things done?

Gr. Jord 

You could use the SetSteps per Unit button on the settings page (just above the reset button). Personally I prefer calculating the numbers but as long as your measurements are accurate when using the Set Steps per Unit button then you should be close.
Hood

one moment i am looking for it.
thank for your quick response

gr. jord

one moment i am looking for it.
thank for your quick response

gr. jord

See the scrrenshot below for the buttons location.
Hood

thanks this will work I think, I will let you know if it's ready.
Going to bed it's 01:20 in the morning.
see you soon.

jord