The International System (SI) of Units The International System (SI) of Units comprises seven clearly defined units. Namely, length, mass, time, electrical current, thermodynamic temperature, amount of substance, and luminous intensity, from which the base units of meter (m), kilogram (kg), second (s), ampere (A), kelvin (K), mol (mol), and candela (cd) are derived. Other units, known as derived units, can be determined from the seven base units. Together with the progress of science and technology, it is essential that these units and their specifically expressed standards keep pace with the high precision of the times. Various countries are already well advance in standards research, and it is therefore possible to continue research on increasing the precision of these standards. Of the seven base units, NRLM conducts research on length, mass, time, thermodynamic temperature and amount of substance. Back to the Measurment Standards HomePage