Wise to use digital, should be more precise than an mechanical but not necessarily any more accurate than a good one used correctly, as you have found
I have a set of digital pressure calibrators accurate to 2 decimal places (+/- 0.1% at full scale) and calibrated to national standards - not for air gunning as such but as part of my work.
You would be amazed at how far out some of the Rifle/bottle/checker gauges are when I have checked them.
Not so bad if you know the error and just want the same thing every time but useless if you want to get a known pressure reading.
Makes me chuckle when I look at the gauges normally supplied with reg checkers, you would be lucky if you got an accurate one but with such a small face/accuracy (probably quoted as 4% or maybe even 5%) and a needle that is probably 3 Barg wide, confidently saying your reg is set to 85 Barg is a bit of a push.