A system of physical units based upon the use of the meter, the metric ton (or tonne: 10⁶ grams), and the second as elementary quantities of length, mass, and time, respectively. In this system, density is expressed in tonne m⁻³, velocity or speed in m s⁻¹, force in tonne m⁻² (or sthene), pressure in centibars (or pieze), and energy in kilojoules. The mts system is used primarily by European engineers.