The metric system is a number of different systems of measurement with length based on the metre, mass on the gram, and volume on the litre. This system is used around the world. It was developed in France and first introduced there in 1795, 2 years after the execution of Louis XVI. The metric units are based on decimal groups (multiples of ten). At first the metric system was based on two quantities: length and weight. The basic units were called the "metre" and the "gramme".