@Tech@ZWO#59326 We will appreciate it if you can tell us more details.
Add a "Step Setting" button to the Guide Setting window (or automatically recalibrate when you notice that the mount or guide camera or guide focal length or guide speed had changed).
When that button is invoked, test the PHD2 calibration so that a guide star will on average move about 2 pixels per calibration step. Use this scale as the Calibration Step size. (I.e., so that PHD2 finishes the 25 pixel calibration in about 12 steps).
For the Max RA and Max Declination step sizes, you will need to know the maximum of the first derivative of the periodic error curve of the mount (ask your Andy Meng, and he should be able to explain why to you). Set the Max RA and Max Declination step sizes so that the value is just sufficient to correct for this first derivative error.
Chen
