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A hair's breadth, or the width of human hair, is used as an informal unit of a very short length.〔(【引用サイトリンク】title=Hair's breadth (hare's breath) )〕 It connotes "a very small margin" or the narrowest degree in many contexts.〔(【引用サイトリンク】title=Hairs breadth )〕〔(【引用サイトリンク】title=Hairs breadth )〕 Until the middle of the 20th century, the highest resolution of measurement was considered to be the same order of magnitude, around 10−5 metres, as the diameter of a human hair. A "hair's breadth" was, and still is, informally, a very small measurement. ==Definitions== This measurement is not a precise one. Human hair varies in diameter, ranging anywhere from 30 μm to 100 μm. One nominal value often chosen is 75 μm, but this – like other measures based upon such highly variant natural objects, including the barleycorn – is subject to a fair degree of imprecision. Such measures can be found in many cultures. The English "hair's breadth" has a direct analogue in the formal Burmese system of Long Measure. A "tshan khyee", the smallest unit in the system, is literally a "hair's breadth". 10 "tshan khyee" form a "hnan" (a Sesamum seed), 60 (6 hnan) form a mooyau (a species of grain), and 240 (4 mooyau) form an "atheet" (literally, a "finger's breadth"). Some formal definitions even existed in English. In several systems of English Long Measure, a "hair's breadth" has a formal definition. Samuel Maunder's ''Treasury of Knowledge and Library of Reference'', published in 1855, states that a "hair's breadth" is one 48th of an inch (and thus one 16th of a barleycorn). John Lindley's ''An introduction to botany'', published in 1839, and William Withering' ''An Arrangement of British Plants'', published in 1818, states that a "hair's breadth" is one 12th of a line, which is one 144th of an inch (a line itself being one 12th of an inch). Winning a competition, such as a horse race, "by a whisker" (that is 'by a hair') is a narrower margin of victory than winning "by a nose." An even narrower margin might be described in the idiom "by the skin of my teeth," which is typically applied to a narrow escape from impending disaster.〔(【引用サイトリンク】work=The phrase finder )〕 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「Hair's breadth」の詳細全文を読む スポンサード リンク
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