I've done several. You really have to be careful. If the lettering on the glass is sharp and crisp white in color, it's in pretty good shape. A dry microfiber cloth is ideal, but I rarely find that works sufficiently. You almost always need a bit of liquid to remove the schmutz and get the glass looking new. For that, I've always sprayed a conservative amount of 409 on the towel and very carefully cleaned both sides of the glass. It's impossible to do this and not contact the lettering. Proceed slowly and buff the liquid off as you go to keep reapplication to a minimum.
OTOH, if the lettering has browned, like from sun exposure, it'll come right off the glass before you realize it's happened. So use your judgement and don't be in a hurry. Better to discover that on one of the corners versus right in the middle of the scale.
Cleaning off the rear of the glass faceplate is equally as important. Before you attempt that, you should look closely at the weatherstripping. If it's all dry rotted, it's simple to knock bits of it off accidentally as you're cleaning. When you do that, you typically smear these tiny pieces into the glass as you're cleaning. Those smears can't be removed with liquid but a sharp razor blade will make short work of them. However, it's easy to get careless with the razor blade as you make your way around the glass and gouge a chunk out of the paint. I've done this more than once and am always like - I can't believe I just did that! Fixing the paint on these straight lines is a massive PITA so don't make that mistake.
When finished, the unit will have better light dispersion through the scale and look just stunning.
. Why do I think of this situation every time I ever so gently clean a dial glass
