|≈||approximately equal to|
|digits||indicates that digits repeat infinitely (e.g. 8.294 369 corresponds to 8.294 369 369 369 369 …)|
The femtometre (American spelling femtometer, symbol fm derived from the Danish and Norwegian word femten, "fifteen"+Ancient Greek: μέτρον, metrοn, "unit of measurement") is an SI unit of length equal to 10−15 metres, which means a quadrillionth of one. This distance can also be called a fermi and was so named in honour of physicist Enrico Fermi, as it is a typical length-scale of nuclear physics.
A pace is a unit of length consisting either of one normal walking step (~0.75 m), or of a double step, returning to the same foot (~1.5 m). Like other traditional measurements, paces started as informal units but have since been standardized, often with the specific length set according to a typical brisk or military marching stride.