Both the metric system and the International System of Units (SI) are important. The SI system is the modern form of the metric system. It is the most widely used measurement system. It is built of seven base units. It has twenty-two named units and includes many more unnamed coherent derived units. The metric system is a decimal system of measurement that is internationally recognised. It was based on the French "metre des Archives". The metric system has been improved, refined and extended to include many more units.
