A car can measure its speed in kilometers per hour without having to travel for an hour. The choice of units is completely arbitrary and is ultimately a matter

A car can measure its speed in kilometers per hour without having to travel for an hour. The choice of units is completely arbitrary and is ultimately a matter of taste. Most people know what a second is, and that a billion years is a really long time. They probably have no idea what a picosecond is. Clock experts generally use fractional frequency errors which have no unit at all.