Myself and my mother are the only ones in the family not needing glasses. In 2011, I started getting headaches. I also was not able to read the tiny tiny print on an iPhone, which had never been an issue (just move it closer). Research on the net showed that I probably had Presbyopia. I printed out the little page.
Print this out:
https://www.aclens.com/global/lensimages/pdf/reading-strength.pdf
Use it at various distances for common tasks. You will see which strength for what application.
And Stomachmonkey is corret. Buy the big packs for cheap on Amazon and spread them around the house, car, office, etc. Buy extras, cause the cheap ones break...