Click here to purchase the entire book in PDF format. SI Every four years there is a meeting held in Paris with representatives of the governments of 51 countries who are part of a group called the Metre Convention. This meeting is called the Conférence Générale des Poids et Measures or CGPM. This group oversees a standard set of measurements for things like time, mass, and distance, just to name a few. That set of measures is called the Système International d'Unités or SI, although most normal people call it the metric system.