Systems of units

Abstract

Any system of units defined in terms of the fundamental units of mass, length and time form an absolute system of units. The principle of absolute units was first proposed by K. F. Gauss (1777–1855) in 1832[1]. In 1851[2], he and Weber drew up a set of units based on the millimetre, the milligram and the second. This is known as the Gaussian system. Twenty-two years later[3] the British Association adopted the metric system but used the centimetre, the gram and the second as the fundamental units; these are often called the CGS units. The metric system recommended today is the International, or SI, system. This is based on the metre, kilogram and second. Engineers throughout the English speaking world generally use the foot, pound, second units. The history of the fundamental units is given briefly by Sir Richard Glazebrook in the 1931 Guthrie Lecture[4] and in some detail by R. W. Smith in the National Bureau of Standards Circular 593 entitled the Federal Basis for Weights and Measures[5]. The definitions of the seven SI base units are given in the National Physical Laboratory publication entitled The International System of Units (1977).