As the peak error can be affected by any number of sporadic things (sudden spike in seeing, glitch in mount tracking etc),
The whole point of using Dec with guiding turned off is that it doesn't produce any guiding spikes because the axis is not moving and there is no guiding happening. All you see then is pure atmospheric motion which you want to avoid trying to chase.
You say that you have seen peak Dec errors of 3.71 arc seconds. Well the fact is that this error happened in the past and the next measurement may show a different position of the star, but the guiding software will still try to move the mount by that amount of distance, even though the actual star position may now be in the opposite direction.
From: stephenjwinston@... [ap-gto]
Sent: Tue, Jul 10, 2018 9:46 am
Subject: Re: [ap-gto] Re: Things that customers do that drive me nuts on CN
I wanted to come back to the "right" way to use GA to determine the MinMo values, as I agree it is critical that these be set correctly.
Specifically for setting DEC MinMo you wrote:
>Look at Peak DEC error. It gives it to you in both pixels (which you need for PHD MinMo) and Arc-Seconds (which you need to talk to people with).
>Set MinMo to Peak DEC error value GA gave you
I'm not sure if you really meant "peak" here. ; I've uploaded a screen grab of my calibration run last night. During GA the measured peak DEC error was 1.25px or 3.71 arc-s. As the peak error can be affected by any number of sporadic things (sudden spike in seeing, glitch in mount tracking etc), I don't think it provides the right baseline to set DEC MinMo.
The RMS number gives a better measure. I have seen suggestions to set MinMo to 2x the RMS which was 0.12 px / 0.36 arc-s for me, so that would have put my DEC MinMo at 0.24 px. Perhaps the right multiplier needs to be bigger at 3x or even 4x the RMS.
As I mentioned in an earlier post, Bruce already agreed that the current MinMo recommendations can be too optimistic/aggressive. Having PHD2 come up with more realistic recommendations will help (especially beginners) get off to a good start.