What also works is just dropping a little water on it, after first using a damp stick with a rag tied to remove dust/spider webs/mud. Read fast, before it dries off.
I used to work maintenance at a mobile home park, and had to read ~190 below-ground water meters every month (plus some 40+ ones located under the mobile behind the skirting). Another guy read the other 200+ below-ground water meters (sometimes we switched off, just to have it less boring).