I was given the following information via email.

"I have tried both methods of re-zeroing a winter vario. The
adjustment wheel's behind the little winter emblem...loosen the small
screw and it will rotate out of the way and you can get to it. But, it
is easy to bend things you should not bend. I prefer the small (very
small!!!) drop of clear fingernail polish. Get the brush almost dry
before you touch the needle. It doesn't take much. After it dries,
recheck the zero...as the evaporation of the solvent in the polish will
change the finished weight."