A reading guide. The order is suggested; each article stands on its own.

A saw sings when its blade is bent. Two different chords have the same interval inventory. A composer asks a player piano to maintain a tempo ratio that no pair of integers can express exactly. These articles begin with such specific problems and follow the mathematics far enough to explain what is happening.

Beauty is the reason for collecting them, not a quantity they all claim to measure. Some concern a physical mechanism, some a mathematical construction, and some an experiment on a listener. Keeping those questions distinct leaves room for the connections between them.