In a sequence of observations of Mars (using Sidereal tracking) we sought to learn if there is a periodic error in the tracking. We plot the pixel coordinates of Mars in the session covering several hours:

What is most evident is that Mars drifted relative to the frame – but this may be the actual motion of Mars, although it seems a lot (Mars moves in RA mostly, not DEC – i.e. Y). This can be checked against the position of the stars in the frame – more later.