Editing Torr (section)

==Conversion factors==
The millimetre of mercury by definition is 133.322387415 Pa<ref>{{Cite book |title=BS 350: Part 1: 1974 – Conversion factors and tables |date=1974 |publisher=[[British Standards Institution]] |page=49 }}</ref> (13.5951 g/cm<sup>3</sup> × 9.80665 m/s<sup>2</sup> × 1 mm), which is approximated with known accuracies of density of mercury and [[standard gravity]].

The torr is defined as {{sfrac|760}} of one standard atmosphere, while the atmosphere is defined as 101325 pascals.  Therefore, 1 Torr is equal to {{sfrac|101325|760}}&nbsp;Pa. The decimal form of this fraction ({{gaps|133.322|{{overline|{{gaps|368|421|052|631|578|947}}}}}}) is an infinitely long, periodically repeating decimal ([[repetend]] length: 18).

The relationship between the torr and the millimetre of mercury is:

*1 Torr = {{gaps|0.999|999|''857''|''533''|''699''|...}} mmHg
*1 mmHg = {{gaps|1.000|000|''142''|''466''|''321''|...}} Torr

The difference between one millimetre of mercury and one torr, as well as between one atmosphere (101.325&nbsp;kPa) and 760&nbsp;mmHg (101.3250144354 kPa), is less than one part in seven million (or less than 0.000015%). This small difference is negligible for all practical purposes.

In the European Union, the millimetre of mercury is defined as<ref>[https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:31980L0181 Council directive 80/181/EEC] (20 December 1979)</ref>

:1 mmHg = 133.322 Pa

hence

*1 Torr = {{gaps|1.000|00''2''|''763''|...}} mmHg
*1 mmHg = {{gaps|0.999|99''7''|''236''|...}} Torr

Other units of pressure include:

* The bar (symbol: bar), defined as 100 kPa exactly.
* The atmosphere (symbol: atm), defined as 101.325 kPa exactly.

These four pressure units are used in different settings. For example, the bar is used in meteorology to report atmospheric pressures.<ref>Note that a pressure of 1 bar (100000 Pa) is slightly less than a pressure of 1 atmosphere (101325 Pa).</ref>  The torr is used in high-vacuum physics and engineering.<ref>Cohen E. R. ''et al.''  [https://books.google.com/books?id=TElmhULQoeIC Quantities, Units and Symbols in Physical Chemistry], 3rd ed.  Royal Society of Chemistry, 2007 {{ISBN|0-85404-433-7}} ([http://www.iupac.org/publications/books/gbook/green_book_2ed.pdf  IUPAC pdf copy]).</ref><ref>DeVoe H. Thermodynamics and Chemistry. Prentice-Hall, Inc., 2001, {{ISBN|0-02-328741-1}}.</ref>

{{pressure Units}}