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Time Lord, 6 thou is not too bad really. I have some fittings that are more like +20 thou. Focusers are probably machined to something like 1.255 -0/+010, or maybe +.005.
How would 1.252 at 20deg C focuser go operating at 2deg C with a warm EP barrel?
AS for the 3 positions used with the Laser, since you have ascertained the laser is centred within the body, and you are clamping the tube against the same point in the focuser with the lock screw I doubt that this proves anything.
As for which method is the more accurate, I think you can best judge that by a comparison of detail visible on Jupiter or Saturn's rings. There is software available that will measure colimation, but it is not really meant to be used with a dob, and it needs a digital image of a star.
HTH,
Doug
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