Hint, when buy glasses ask about swim goggles - they will write down the PD distance (since they don't have swim goggles), and then you can keep that number. You still need to buy one final set of glasses, but you can get their cheap frames and be done.
This life hack really isn't necessary, you can just ask for your PD distance and they'll bring out a little machine that measures it. No optometrist has ever been weird about it, a few have even told me a few sites to get cheaper glasses.
My optometrist was weird about it, presumably because he also sells frames and lenses. I went to an optometrist who doesn't sell frames or lenses and she was happy to spend less than a minute to measure my PD. I won't be going back to the former.
I go to Walmart Vision. They do all the measurements and write down everything without complaining at all for (I think) about $70. Then order a few pair from Zenni and restock every 5-7 years.
