To calibrate you machine -
Have a look at the setting for the motors as they are set - or set them at a reasoanble figure to start with.
Move the axis by one inch on the DRO , measure the ACTUAL movement of the axis.
The number of steps per inch is equal to the number of steps the machine is set to, divided by the distance the axis actually travelled.
Bear in mind stepper motors are usually 1.8 degress - i.e. 200 steps per rev,(multiplied by motor settings - e.g. 1/8 step or whatever) multiplied by any step down you have to your axis, multiplied by the number of turns per inch - so it is usually a round figure - in my case 64,000 - so if your answer above comes out to 63,995 - give it the benefit of the doubt.