By the barometric formula, 1 bar is roughly the atmospheric pressure on Earth at an altitude of 111 metres at 15 °C. The bar and the millibar were introduced by the Norwegian meteorologist Vilhelm Bjerknes, who was a founder of the modern practice of weather forecasting.

Where does millibar come from?

Millibar is a metric unit of pressure mainly used in European countries and is derived directly from the bar pressure unit which equals 1,000 mbar. In SI units 1 mbar equals 100 pascals.

Who invented the bar pressure?

This is in contrast to the well-known unit of pressure, atmosphere, which now is defined to be 1.01325 bar exactly. As a rule of thumb, a bar is (almost) equal to an atmosphere. The bar and the millibar were introduced by the British meteorologist William Napier Shaw in 1909.