Understandable of course, and that jig and measuring is great too. I believe I saw a string method before too. I kinda wondered how much a mm or two would be noticed if at all for a casual rider going less than 30 mph.
Rear dropout spacing already almost 122mm, so when closing skewer is it assumed the 2mm difference would be taken up evenly from both sides? One could measure with no wheel mounted, and then locked in at 122 I guess to see, but that is probably greater precision than I could measure.
Perhaps I will look into Sheldon site for string method, but would have to take off fender too. I may just try one DS spacer and be happy dropouts aren’t spread or compressed. Recentering the axle then would then leave an equal axle protrusion of maybe 3.5-4mm.