The torr (symbol: Torr) is a non-SI unit of pressure defined as of a standard atmosphere, chosen to be roughly equal to the fluid pressure exerted by a millimeter of mercury, for example a pressure of 1 Torr is approximately equal to 1 mmHg. Note that the symbol is spelled exactly the same as the unit, but the symbol is capitalized, as is customary in metric units derived from names. It was named after Evangelista Torricelli, an Italian physicist and mathematician who discovered the principle o… (More on Torr)