Measurement is one of the hallmarks of civilization. How far is it? How much does it weigh? What time is it? These are all questions that we hear every day. Indeed, asking the time is probably the number one question that we ask, especially when we are doing something we don't like!

Simple units, such as the cubit, which is the distance between a man's elbow and the tip of his middle finger, or the span, the distance from the tip of the thumb to the tip of the little finger of an outstretched hand, were used for much of recorded history. After all, the human body is always available for measuring distance. But it does suffer from one inherent problem. Not all men are created equal! Some are taller than others so that not all forearms are the same length.

Of...