The ratio of the length of a pie’s crust to the length of a slice of that pie is denoted 🥧 and pronounced “pie”.

pie
circumference	🥧 r
area	½ 🥧 r²
sphere
surface area	2 🥧 r²
volume	⅔ 🥧 r³

See also: The Tau Manifesto by Michael Hartl. Brought to you by Clockwork Worlds.