Yes, I did mean the Earth's rotation. I thought it was probably done by the telescope but didn't realise how much calibration was involved.Do you mean rotation of the Earth? For that my telescope is on a driven equatoral mount, I have to point the polar axis of the mount as close as possible to the north celestial pole, then I have to do a two star alignment and 4 calibration stars, it takes a long time. The 4 calibration stars arn't necessary but it helps to improve the tracking and the Goto.