Fair enough, usability will obviously be poor if the scale is difficult to read. My eyesight is terrible but at least it is still all myopia so I can compensate by putting the calipers extremely close to my eyes. Looks awkward and people call me Mr. Magoo but it works!
I just bought a digital caliper with a big LCD display. It will work with Imperial or Metric units, which I really like.
My analog calipers are Imperial. I love them, but run into Metric units a lot. Got those in '88 and they are still calibrating in spec and working great. No battery. Did need light oil and cleaning a decade ago.
I have one Vernier caliper and... it is getting hard to read in some conditions. Bummer. I still prefer these in longer forms, say greater than 12"