I need a +3 or +4 to read, and normally wear a vari-focal. I tried the vacuum type plastic stick-on lenses, the first time I lost them, was in a soak tub, fortunatly I recovered them, the second time some one took my mask off on a rescue practice in the sea, that was £35 lost I don't think I had them three months;-0 I have a mask with bi-focal lenses cemented in, I find they are set to low in the mask to be much use, and struggle to use them to read instruments. I have seen masks with separate angled down bottom lenses, I heard the bottom lens is normaly partialy covered with water so its not very good.
As I have been unable so far find satisfaction using lenses, I have been looking for the alternative of large bold print numerals on gauges.
I have got an apex pressure gauge, its okay, I can read it without problem, though I sometimes struggle to read a buddy's. I am on the look out for a compass with real big numerals, I have got a couple of suunto's compasse's, they are not legible enough, I can preset the bezel and read the lubber line, but not the bearing numerals. The main reason I didn't buy a Suunto computor was I couldn't read the numerals.