Torr (torr - Mercury), pressure
The torr (symbol: Torr) or millimeter of mercury (mmHg) is a non-SI unit of pressure. It is the atmospheric pressure that supports a column of mercury 1 millimeter high. The unit is named after Evangelista Torricelli, Italian physicist and mathematician, for his discovery of the principle of the barometer in 1643. A related unit is the micrometre of mercury (µmHg), which is one thousand times smaller.