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I do not think loupe is the best to use for edge monitoring, at least for me too small of aperture.
I like to use a scope with light source, it gives me good enough magnification and resolution to...

You can search for tests that work to tell when the bevel is set, I personally like to use a scope, others like TPT, or TNT or shaving arm hair.
All those work so you have a choice what to go with...

This is not quite correct, the sharpie mark will be gone but that does not mean the bevel is set.
You have to have other ways to tell the bevel is done, i.e no micro chips, if there is pitting on...