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.

https://c1.staticflickr.com/5/4620/25840583328_42e8c52c80_b.jpg

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.

https://www.google.com/logos/doodles/2017/ferdinand-monoyers-181st-birthday-5105939098107904.4-2xa.gif