The two most common measurement systems used in the United States are the U.S. Customary System and the International System of Units (SI system, or the metric system). While the United States uses both systems, many other countries have adopted the SI system exclusively. There are seven base units. They represent the quantities of length, mass, time, electric current, thermodynamic temperature, amount of substance, and luminous intensity. One of the most beneficial aspects of the SI system is the ability to multiply the base unit by powers of 10 to express multiples or sub-multiples of the base unit.