Length - Length is the distance between one point in space to another. Over the ages there have been many units of length. Today the most commonly used units are the kilometer, meter and centimeter and the mile, the foot and the inch. Originally the meter was supposed to be an absolute measurement. And in fact the meter was supposed to be one ten millionth of an arc of the earth measured from the pole to the equator. In fact they did not get the value quite correct (0.2mm short) and is now redefined as the length at 0^oC of a certain length of platinum rod kept in the Archives of Paris. In a similar manner the yard is defined as the distance between two marks on a certain bronze bar at 62^oF kept by the Board of Trade in London. The other units of length are multiples of these fundamental units of length.

Further Information on this Topic can be found in the books of R.P.W. Scott by following the listed links