Paul,
PA isnt bad just the scatter is a concern.
With that amount of scatter your PA result is in the noise zone anyway.
You will be going back and forth each time you do a new run !
The screen shot you provided lists that you have 11 terms in use.
I would think that is too many for that level of uncertainty and that small number of points, the extra terms will probably be doing more harm than good, but not that bad that the RMS be at 164 - ie to say its not the main cause.
Print out the Fit Information Dialog Box so we can see what they are and what they are doing.
Try removing all but the standard terms and get the polar alignment sorted out first before adding all extra terms.
You really only need just a few mapped points more than the bare minimum (6) to get PA pretty accurate - 10 should be more than enough for the first physical PA adjustment. 6-8 for a first PA should work.
RMS (164 arcsec) is high because the scatter is widely spread.
You need to think about the cause of this and fix it in order to get the RMS lower, its not going to go away by itself just because you have a Tpoint model.
The scatter diagram shows a definite North/South spread so its not across all axis - flexure in your imaging train maybe ?
Wind, vibration, backlash, (PE ? not sure) etc could all be possibilities.
Are these mapped points across both meridians ?
Try mapping just on one side and see if the scatter is more localised before doing the second side.
Are you deleting the old model after manually adjusting PA ? - Just a thought !
What is the orientation of your camera with respect to North/South and East/West ?
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