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The torr (symbol: Torr) is a unit of pressure based on an absolute scale, now defined as exactly of a standard atmosphere. Thus one torr is exactly pascals}} (~133.3 Pa). Historically, one torr was intended to be the same as one "millimetre of mercury". However, subsequent redefinitions of the two units made them slightly different (by less than ). The torr is not part of the International System of Units (SI), but it is often combined with the metric prefix milli to name one millitorr (mTorr) or 0.001 Torr. The unit was named after Evangelista Torricelli, an Italian physicist and mathematician who discovered the principle of the barometer in 1644.〔Devices similar to the modern barometer, using water instead of mercury, were studied by a number of scientists in the early 1640s (see (History of the Barometer )). Torricelli’s explanation of the principle of the barometer appears in a letter to Michelangelo Ricci dated 11 June 1644.〕 ==Nomenclature and common errors== The unit's name "torr" is written in lower case, while its symbol ("Torr") is always written with upper-case initial; including in combinations with prefixes and other units, as in "mTorr" (millitorr) or "Torr·L/s" (torr-litres per second).〔 (【引用サイトリンク】url=http://physics.nist.gov/cuu/Units/rules.html )〕 The symbol (uppercase) should be used with prefix abbreviations (thus, mTorr and millitorr are correct, but mtorr and milliTorr are not). The torr is sometimes incorrectly denoted by the symbol "T", which is the SI symbol for the tesla. The misspelled symbol "Tor" is also encountered, and is always incorrect. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Torr」の詳細全文を読む スポンサード リンク
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