Metre Convention , also known as the Treaty of the Metre, is an international treaty that was signed in Paris on 20 May 1875 by representatives of 17 nations. The treaty set up an institute for the purpose of coordinating international metrology and for coordinating the development of the metric system. The treaty also set up associated organizations to oversee the running of the institute. Initially it was only concerned with the units of mass and length but, in 1921, at the 6th meeting of the General Conference on Weights and Measures (CGPM), it was revised and its mandate extended to cover all physical measurements. In 1960, at the 11th meetings of the CGPM, the system of units it had established was overhauled and relaunched as the "International System of Units" (SI).