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I use laser to check everything is not grossly out, then refine with cheshire and autocollimator.
On a different, but related matter, how are the primary mirror support springs? If they are a bit weak, the mirror can move/sag and collimation change as you elevate the tube. Either replace them with firmer springs (Bunnings) or screw all three collimation screws up tighter to put the springs under greater compression.
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