History
In metal type, the point size (and hence the em) is measured as the height of the metal body from which the letter rises. In metal type (possible overhangs aside), 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.
Read more about this topic: Em (typography)
Famous quotes containing the word history:
“The history of every country begins in the heart of a man or a woman.”
—Willa Cather (1876–1947)
“These anyway might think it was important
That human history should not be shortened.”
—Robert Frost (1874–1963)
“Both place and time were changed, and I dwelt nearer to those parts of the universe and to those eras in history which had most attracted me.”
—Henry David Thoreau (1817–1862)