It's for testing your glasses, not your eyes.
But can probably solve the other way around too.
Late addendum to idea following perplexed responses:
You find an old box of glasses of yours or you inherited it from someone. Or you own a secondhand store and want to sell online all of those glasses that you received from the guy who inherited the box of glasses. And you want the correct details for each pair.-- pashute, Apr 20 2023 Prescription Lens Scanner app https://play.google...sses&hl=en_US&gl=US [scad mientist, Apr 25 2023] It's a trick post, he's really testing our comprehension.-- AusCan531, Apr 21 2023 // testing your glasses, not your eyes.
I don't 'see' the distinction ('see' what I did there?). Anyway what if your eyes suck, do you have to wear glasses to wear the test glasses?-- tatterdemalion, Apr 21 2023 //you have to wear glasses to wear the test glasses// Clearly (heh) the 'R' in the invention name stands for 'Recursive'.-- Sgt Teacup, Apr 21 2023 Please see the clarification in the newly edited idea.-- pashute, Apr 24 2023 I believe the optometrists have a widget they can do this with already ...-- normzone, Apr 25 2023 Seems like you ought to be able to make an app for that. Position your smart phone one foot from a piece of paper with writing on it. The app has the camera autofocuses on the paper and reads the focus setting from the camera. Then the user puts the lens of the glasses to test in the way exactly 1" from the camera lens. Camera autofocuses again, reads the focus setting, does some math and gives you the answer...
Funny thing, whenever I say, "it seems like you could make an app for that", if I Google it, someone already has. That still holds true. See link for the free Prescription Lens Scanner app available for Android or Apple. There were several other options as well, but this was at the top of the list...-- scad mientist, Apr 25 2023 [scad mientist]; exactly what I said back on [pashute]'s "WhatsThapp junk recognition app". I never got as far as hunting for an existing version. Using both a phone & computer together is a clever idea.-- neutrinos_shadow, Apr 25 2023 random, halfbakery