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Normally, text size specifies the height of the font's em square, not a measure of the actual glyphs, such as the height of the capitals. Sometimes, it is desirable (especially among sign cutters) to specify text size in terms of cap height. This script allows the user to select a range of text and set its size by capheight. Capheight is assumed to be the height of the capital M outline.
Download the script and be happy that James made it.
You are welcome, hensleyfx.
What am I missing?
So you'll know:
What you're missing is that it would be fairly useless for type size to be defined as the height of the characters. Because fonts are graphic designs, they vary wildly in shape and proportion. You would therefore have to answer these questions:
Which character's height do you want to be used as the defintion of "size"?
What if that character is rounded at the top or bottom? (Curved edges are always enlarged somewhat to compensate for the eye's natural tendency to view them as "smaller".
What if that character has vertical serifs and the others don't?
What if that character happens to be of a swash design, intended to extend above the "cap height" and/or below the baseline?
What if the typeface is an italic, an uncial, a script? They would look out of proportion to text of more "normal" proportions set on the same lines. (Some do anyway, but at least there's a mechanism to control it should the type designer choose to.)
Clearly what is needed is some kind of relative measure reference. And that's what we have in electronic type: the em square.
The em square is an invisible (imaginary, really) space upon which the character outline is positioned. I say "upon" and not "within" because the character is not necessarily confined to the bounds of the em square. That's how, for example, we enjoy the ornate swashes of the capitals in Bickham Script.
That's also why, when refering to electronic typefaces, the necessity of the em square really has nothing to do with its being some kind of archaic throwback to the days of physically cast type, as many are prone to trot out whenever the subject comes up. (Clearly, the characters did not extend beyond the bounds of the metal on which they were embossed.)