If you have an external focuser there is simple way to measure the approximate "Microns Per Step" value which gives how many microns the focuser will move for one step of the motor.

Here are the steps:

1. From Gear Tab, Focuser section start to move the focuser in "Out" direction till you see that focuser is moving.

2. Measure the position P1 like on the image:

3. Enter Step Size 500 and click on ">" button to make movement of 500 steps in "Out" direction

4. Measure the position P2 like on the image:

5. The formula K = (P2 - P1)/500 gives how many millimeters are moved per one focuser step (if you have used other Step Size in point 3, replace 500 with the used value). So we have K = (24.64-23.09)/500 = 0.0031. To convert to microns multiply by 1000 and we get 3.1 microns per step.

The full formula is M = ((P2 - P1)/500)*1000.

Note: It is important to work in Out direction only as the backlash will be compensated and you can use slight force over the caliper to measure P1 and P2 more precisely without worrying about focuser play.