An extract on #gunde1fotograf
At the close of the 19th century three different systems of units of measure existed for electrical measurements: a CGS-based system for electrostatic units, also known as the Gaussian or ESU system, a CGS-based system for electromechanical units (EMU) and an MKS-based system ("international system") for electrical distribution systems. Attempts to resolve the electrical units in terms of length, mass, and time using dimensional analysis was beset with difficultiesthe dimensions depended on whether one used the ESU or EMU systems. This anomaly was resolved in 1900 when Giovanni Giorgi published a paper in which he advocated using a fourth base unit alongside the existing three base units. The fourth unit could be chosen to be electric current, voltage, or electrical resistance.
In the late 19th and early 20th centuries, a number of non-coherent units of measure based on the gram/kilogram, the centimetre/metre, and the second, such as the Pferdestrke (metric horsepower) for power, the darcy for permeability and the use of "millimetres of mercury" for the measurement of both barometric and blood pressure were developed or propagated, some of which incorporated standard gravity in their definitions.
At the end of the Second World War, a number of different systems of measurement were in use throughout the world. Some of these systems were metric system variations, whereas others were based on customary systems of measure. In 1948, after representations by the International Union of Pure and Applied Physics (IUPAP) and by the French Government, the 9th General Conference on Weights and Measures (CGPM) asked the International Committee for Weights and Measures (CIPM) to conduct an international study of the measurement needs of the scientific, technical, and educational communities and "to make recommendations for a single practical system of units of measurement, suitable for adoption by all countries adhering to the Metre Convention".
On the basis of the findings of this study, the 10th CGPM in 1954 decided that an international system should be derived from six base units to provide for the measurement of temperature and optical radiation in addition to mechanical and electromagnetic quantities. Six base units were recommended: the metre, kilogram, second, ampere, degree Kelvin (later renamed kelvin), and candela. In 1960, the 11th CGPM named the system the International System of Units, abbreviated SI from the French name, Le Systme International d'Units. The BIPM has also described SI as "the modern metric system". The seventh base unit, the mole, was added in 1971 by the 14th CGPM.