My favorite coincidence in this vein involves feet, nanoseconds, and the speed of light. In special relativity, physicists typically work in "geometric units",

My favorite coincidence in this vein involves feet, nanoseconds, and the speed of light. In special relativity, physicists typically work in "geometric units", where c = 1. Measuring length in feet and time in nanoseconds yields c = 0.983571056 feet/nanosecond This is close enough to 1 for most practical purposes.