Well folk by sheer chance I tried to use one of my instruments after being in the box without battery's for 3 months.
How it worked for me.
1 Remove battery,
2 press and hold one button while,
3 Insert battery and wait for 5 secs,
4 Press reset/ zero
If at first this does not work repeat from 1 with another button.
I have tried this on a vernier, a depth Gage, angle box and a axis measure box.
All seem to have the similar reset but different button.
The IC/Chip used seems to be a programmable device of the same type for all these instruments.
Give it a try and let us know.
Trev