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Ving, the position angle measure will be the same, regardless of magnification, but I think you are right that the separation scale will need to be calculated depending on the magnification achieved with your particular scope. My understanding is the the separation scale is not usually expressed in specific units (such as arc seconds) on the reticle, but rather as regular notches, onto which you impose the scale relevant to your scope.
I have been pondering another question, which relates to working out position angle (hereafter "PA"). Obviously this needs to be measured by reference to north. The books I have read about taking PA speak of letting the stars drift across the FOV (ie untracked), with that movement always being from east to west. Once that is established, North can be inferred, and from there, you can take the PA measure.
What I want to know is whether, once you have done the drift test once, and set the reticle up with north at the top, whether you can leave the reticle in that same position, and take the rest of the measures for the session assuming the north in the reticle to be correct. Or, would this only work if you are polar aligned? Do you need to be polar aligned at all?
Maybe I should just get a jolly reticle, and find out by trial and error!?
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