It's mostly binary -- 16 ounces in a pound, 16 drams in an ounce, 8 pints in a gallon, 8 furlongs in a mile, 4 rods in a chain. Then you've got a few odd ones,

It's mostly binary -- 16 ounces in a pound, 16 drams in an ounce, 8 pints in a gallon, 8 furlongs in a mile, 4 rods in a chain. Then you've got a few odd ones, like 10 chains in a furlong or 22 yards in a chain or 3 feet in a yard. In general, the secret to happiness in customary units is to only ever work in a single unit and never convert between them. If you are working in construction, you probably only ever want to deal in inches. Ceilings are 96 or 120 inches tall, doors are 32 or 36 inches wide, etc etc etc. The moment you start using two units at once you are going to have a bad time, so if you pay attention people tend to only use one, even if it confuses people who don't know why doors are 80 inches high instead of 6 feet 8 inches.