my internet file cabinet.
How Many Licks? or How to Estimate Damn Near Anything by Aaron Santos : Uncertain Principles
“ This is a short little book— 176 pages total— built around the idea of Fermi Problems, the order-of-magnitude estimates that Enrico Fermi was famous for. The idea is that, with a little basic knowledge and some really simple math, you can come up with ballpark estimates of all sorts of things— the canonical Fermi problem example is “How many piano tuners are there in Chicago? ”