METRIC SYSTEM

A decimal system of measures and weights with the meter and the gram as bases. The units of the metric system at the outset were all derived from the unit of length, the Meter, which was intended to be, and is very nearly, one ten-millionth part of the distance measured on a meridian of the earth from the equator to the pole, being equal to 39.37 U.S. inches or about 3 feet 3-3/8 inches. Upon the meter were originally based the other primary units of measure: the square meter (area), the cubic meter (volume), the Liter (liquid volume), and the Gram (mass and weight). It was found, however, that masses could be compared with a higher degree of accuracy than that with which volumes could be determined, and it was therefore preferable to have a material standard of mass specifically defined rather than one derived from the unit of length through the unit of volume. A definite mass, the International Prototype Kilogram was, therefore, adopted as the standard of mass, and the unit of volume, the liter, was then redefined in terms of the standard of mass; the liter being defined as the volume of a kilogram of pure water at the temperature of its maximum density (4°C or 39.2°F), and equal to 1.000027 cubic decimeters. Also see Avoirdupois Weight.