Yeah, well. A few years ago I accidently discovered that the 6" rule(r)s (there now, that should satisfy both camps) I had aquired over the years did not match. Strangely, it was the Rabone Chesterman that was most out - unless that one is right and all the others wrong.
I then discovered a discrepancy between the metric micrometer and dial gauge. Next I bought the 25mm, 50 & 75mm Mitutoyo micrometer standards and tested all my stuff. The end result was that one digital vernier was worse than useless, the other one was consistently low, the dial gauge vernier was also low, whilst the metric micrometer was 0.005mm high at 25mm and a slide vernier (0.05 resolution) was dead accurate (as far as I could tell). In addition, the digital devices eat batteries - there is a website somewhere which compares battery usage rates with Mitutoyo being the best, and surprisingly, that none of them actually stopped taking current when switched off.
I now use the micrometer, followed by the slide vernier (within reason), followed by a new Starrett dial gauge (0.01 resolution), and lastly the better of the two digital verniers.
Looking at the digital specs that I have seen, not many I accept, and understanding a little bit about digital electronics, I would not advise anyone to use digital unless they are not bothered about the least significant digit (this, due to the electronic circuitry, will always have an error of 1 either side of the correct reading).
Regards,
Peter G. Shaw