Reading glasses

I bought my first pair of glasses with non-zero optical power last week: 1.0 dioptre reading glasses. These Twist readers are cheap ($20) and fold flat, which is a pretty cool feature. I chose yellow-green frames to help protect them from getting accidentally crushed.

I had to remind myself what a dioptre is: it's the reciprocal of the optical length (in meters) of a lens, m^-1. This unit of measurement is the work of Ferdinand Monoyer, a French ophthalmologist. A Google doodle on May 9, 2017 commemorated Dr. Monoyer's work on his birthday.