[Fiji Hill]

Millibars are SI units.

Do you mean metric units?

[EEGator]

SI = System International

Le Système international d’unités

[Ophiucus]

SI units are the International System of Units. Basically after WWII, the science community got tired of all the different systems of measurement, including different nations using different metric systems. So, they consolidated everything so that moles, meters, degrees K, etc all meant the same thing for everybody.

[Olog-hai]

Actually, the bar (and “millibar”) aren’t part of the metric system. The pascal is the metric unit of pressure. One bar is supposed to be equivalent to atmospheric pressure at sea level (one atmosphere). In 1982, though, the IUPAC standardized the bar at 100 kilopascals.