The \textit{torr} is a non-SI unit of pressure with the ratio of 760 to 1 standard atmosphere, chosen to be roughly equal to the fluid pressure exerted by a millimeter of mercury, i.e. , a pressure of 1 torr is approximately equal to one millimeter of mercury. Note that the symbol (Torr) is spelled exactly the same as the unit (torr), but the letter case differs. The unit is written lower-case, while the symbol of the unit (Torr) is capitalized (as upper-case), as is customary in metric units derived from names. Thus, it is correctly written either way, and is only incorrect when specification is first made that the word is being used as a unit, or else a symbol of the unit, and then the incorrect letter case for the specified use is employed.