Clark: "I am not buying any more $20 dial calipers. I like my 505-675-51 Mitutoyo dial calipers."
We would all 'like' them; I "like" my B&S caliper but it wouldn't add a thing to my reloading so I don't use it there. The question is would the caliper costing 12-20 time more than we can buy a very good tool for actually matter to a normal reloader? Answer is "NO!" Your needs are obviously more stringent than most of us but you are doing a lot more than simple reloading. You can justify more costly tools; common sense. Ditto it would be foolish for most of us to purchase a tool a machinest would use all day, every day, for our very sporatic and very light use on a loading bench; again, common sense. ??
So far as 'how much accuracy' does anyone 'need' of a caliper, every caliper I've yet examined, costly or inexpensive, has been within a half thou according to my Jo blocks. Calipers are mostly used when trimming cases and seating; anyone thinking he needs better accuracy than .001" for that is kidding himself!
Anyone needing better accuracy than a thou had better use a micorometer because no caliper I know of is manufactor spec'd tighter than that and yeah, that's a possible 2 thou spread but it's still only a potential error
of +/- 1 thou.