In my case I want to center a target accurately enough to place a specific guidestar safely on an oag sensor. This requires setting a specific oag angle and centering the target to match the FOVI layout.
I think my current accuracy with the sgp centering is slightly less than 1', but I can't set the tolerance too small because it may never reach it.
But for me and others with similar issues, the repeatability of the attempt at centering is very good - I think a few arc-seconds. If the centering were working as well as possible, it wouldn't get stuck a bit off from the target - it would zero in on it and start to miss by a small amount randomly around the target location. When that happens you know you are limited by the repeatability of the mechanics and not something that software could fix.
I am all for reporting everyting in arc-seconds - especially HFR for star sizes and errors in centering. It is much more natural to me and although it may not be natural for other people - I think it is to their benefit to think in arc-seconds for guiding, star size - etc. because it is a fundamental unit that translates to different systems. If you get a 'feel' for things in terms of pixels - it only applies to your setup and will be off if you change something.
I realize pointing more accurately than 1' is asking a lot - but I am very much in the spirit of using smart software to get the most out of given equipment - rather than keeping things very simple and accepting adequate performance. I would not want to do something very elaborate that involves a lot of code and modeling - but in this case I think it is pretty simple and would be a win in many ways. If it does somehow unravel and causes crazy new centering problems - that would be unfortunate and it might need to be abandoned - but I wouldn't expect that to happen.
I just wish I could try it now but that will be delayed some days.
Frank