If it has a chuck, chuck up a piece of square stock that you can place a digital protractor on. Take the protractor reading. Us the calibrate function, telling the axis to rotate 10 times (3600 degrees.) Take another protractor reading and then input that into the calibration.
So the rotary axis is set up in steps per degrees. depending on if it is belt driven or what ever the gear ratio is. If your Motor is 200 steps per rotation and you have 10 micro steps thats 2000 steps per rev. Multiplied by lets say 2.3 :1 gear ratio is 4600 / 360 = 12.77 steps per degree.