Re: "em" should be horizontal, "ex" vertical

Peter Flynn (pflynn@imbolc.ucc.ie)
11 Aug 1997 13:38:40 +0100


Date: 11 Aug 1997 13:38:40 +0100
From: Peter Flynn <pflynn@imbolc.ucc.ie>
To: walter@natural-innovations.com
Cc: www-html@w3.org
Message-id: <199708111238.NAA21503@imbolc.ucc.ie>
Subject: Re: "em" should be horizontal, "ex" vertical

>  > Correct, the definition of an "em" is a *square* of any given body size,
>  > ie 9pt*9pt, 24pt*24pt, 72pt*72pt are all ems.
> 
> And here I thought an em was a square the width of an uppercase "M".
> Silly me.

Not silly. It _was_ once the width of an M, at some time in the past
when an M was assumed to be as wide as it was high.

>  > The correct term for a 12pt
>  > em is a *pica* em as pointed out, an em is a relative unit.
> 
> I've never heard of a "pica em" -- only just "pica" (1/6 of an inch), and
> picas are indeed used for both horizontal and vertical.
 
"Pica" is an abbreviation of "pica em". Pica was an old name for 12pt type.
1pc not exactly 1/6", as 1pt is not exactly 1/72" in standard printing:
there are approximately 72.27 points in an inch. But many DTP systems use a 
"big point" of exactly 1/72" for convenience. In short measures this does
not matter much: but over the height of a page it can make a visible
difference. A document system should probably specify what it means by "pt".

///Peter