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An em is a unit in the field of typography, equal to the currently specified point size. For example, one em in a 16-point typeface is 16 points. Therefore, this unit is the same for all typefaces at a given point size. Typographic measurements using this unit are frequently expressed in decimal notation (e.g., 0.7 em) or as fractions of 100 or 1000 (e.g. 70/100 em or 700/1000 em). The name "em" was originally a reference to the width of the capital "M" in the typeface and size being used, which was often the same as the point size.〔 == History == In metal type, the point size (and hence the em) was equal to the line height of the metal body from which the letter rises. In metal type, the physical size of a letter could not normally exceed the em. In digital type, the em is a grid of arbitrary resolution that is used as the design space of a digital font. Imaging systems, whether for screen or for print, work by scaling the em to a specified point size. In digital type, the relationship of the height of particular letters to the em is arbitrarily set by the typeface designer. However, as a very rough guideline, an "average" font might have a cap height of 70% of the em, and an x-height of 48% of the em. 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「Em (typography)」の詳細全文を読む スポンサード リンク
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