I was using printed setting circles program for this...
http://www.startrak.co.uk/MakingSettingCircles.htm
To make the vernier, I printed one set of short tracks (Setcirc.exe, altitude, 70mm) with resolution of 600dpi. as main scale.
Then I printed another set, with resolution of 660dpi, as vernier.
After a bit of cutting with scalpel and gluing with sticky tape and I have good vernier with resolution of 0.1mm for the cost of two sheets of printer paper (or plastic).
It is not digital, but still accurate enough :-)
Edit: picture added for clarity...