Daft question I know (and you may have already answered it, I’m not reading through all that) but why didn’t you just have your eyes tested through the usual channels, ie: go to the med centre and be referred to a contracted optician?
Locally employed opticians provide you with the full details of your required prescription, on the correct MOD form and you even get to keep a copy which you can take into any opticians and have a pair of glasses made up from. Oh and you get a free pair of defence specs, just what is needed to get out Freedom Parades etc. 😉
Of course if you really want that £10 then book a few days off and sit yourself down behind that highly efficient JPA system.
Or next time a fairy is calibrating the flange nuts or something on a Tonka laser designator just have a quick peek in the lens for a bit of cheap and easy laser corrective surgery (caution, this may not actually work).