Maybe my lenses aren't progressive
I've been thinking about it and I might have no line bifocals.
Once upon a time, long, long ago I had glasses made that were just for working at the computer terminal where I sat for 8 hrs. inputting library records for the Washington State Library. That 2nd pair of glasses saved my neck and back and prevented more than a few headaches.
I should never overestimate my basic arithmetic skills.