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RE: Units, font sizing, and zoom suggestion for CSS 3

From: Karlsson Kent - keka <keka@im.se>
Date: Thu, 20 Jan 2000 21:12:06 +0100
Message-ID: <C110A2268F8DD111AA1A00805F85E58DA68531@ntgbg1>
To: www-style <www-style@w3.org>

> Earlier, on this list, Jan Roland Eriksson mentioned the following:
> 
>   http://css.nu/articles/typograph1-en.html
> 
> It says that the "em" has been changing over the years, starting with
> Roman letters that were all capitals (e.g. M), followed by the
> introduction of lower-case letters with descenders (e.g. p), and then
> the advent of accents (e.g. ring above).

While that is a fairly well-written introduction to typographic units,
it is not all-together true.  It limits the "M" definition of em to
ancient Greece, while actually it is 1) in use today, not only in
TeX, and 2) the size of a "unit block" is not normally called an "em".
I can fax pages from recently published (1990-ies) typography books
substantiating this claim (no, I don't currently have a web site
where I can put up scans of those pages).

But the area of typography has never been ruled by strict standards
and the "em-age" varies.  I once did a web search to find definitions
of "em" (attached). As you can see the definitions are very varied
(including equating 1 em and 1 pica).  But most seem to agree that
the original, and in many cases *current*, definition is that it
is the width of an M (or possibly m).  (Likewise do the (Swedish)
typography books have have consulted.  **None** of them refer to
anything like the p height as an "em"; while some of the web pages
I found do.)

So, I would say that there is some confusion, but that an "em"
really is the width of a capital M.

		Kind regards
		/kent k


The following was the result of my (old) web seach.
I haven't checked if the links in it still work.


Skip this if you're not interested:

________________________________________________________


It's a complex world...  The definitions of what is an em and an en vary
somewhat.    A web search came up with the following (see below).   Some say
an em is the nominal type size, some that it is the width of a capital M,
some are schizophrenic enough to say both without qualification (some say
both, but with qualification).  Most say an en is half an em, some say it's
the width of an N (or an n).  Again there are some that are a bit schizo...
(http://channels.microsoft.com/typography/glossary/ch6.htm gives one of the
better qualified definitions)

One site reported that they had found one 0.5 em (1 en?) width suitable for
a particular narrow monospaced Latin font
(http://www.emigre.com/EFoIBMoD.html).  One Japanese typography site
(http://www.fontworks.co.jp/e/typography/talk/004.html) happily used the em
relative unit also for Hn-based characters.



===================================================


http://ourworld.compuserve.com/homepages/profirst/e.htm

em   A unit of relative measurement originally derived from the width of the
letter M. Fonts are scaled so that 1 em =
point size. 

em dash   By definition, a dash the width of an em. 

em quad   See em space. 

em rule   See em dash. 

em space   By definition, a space the width of an em. 

em square   Originally, this term referred to a 2-dimensional rectangle
whose width and height corresponded to the
character width and bounding box height of a letter M in a typeface. Over a
period of time, this definition has mutated to
the point where it can refer to a square whose width and height are both
equal to the character width of the M, or to a
square whose width is a measure of a standard full-width character, or the
widest standard width of a character. The
definition is sometimes further muddied to mean a square whose width and
height is 1000 points in an unscaled PostScript
font and 2048 units in an unscaled TrueType font. The width of the letter M
is by no means fixed in commercial fonts, as
would be suggested by the degenerate definitions. However, the  em space 
of typefaces is most commonly approximately
1000 points (unscaled) in PostScript or 2048 units (unscaled) in TrueType. 

en   A unit of relative measurement originally derived from the width of the
N. 1 en = .5 em. 

en dash   A dash the width of an en. 


http://www.quillandmouse.com/qmdtp.htm#E
                              Em Dash: A dash the width of the character M
for the font and point size in use. Em
                              dashes mark a sudden break in thought, to set
off a summary, or to set off a parenthetical
                              phrase that is very abrupt or includes commas.


                              En Dash: A dash the width of the character N
for the font and point size in use. En
                              dashes are used to indicate a number range.  

[They also say:]
                              Font: While often confused with "typeface,"
traditionally, font refers to a complete set of
                              type for a particular typeface in a particular
size. For instance, 12 point Times New Roman
                              would be a font while Times New Roman would be
the typeface.  


http://www.binarygraphics.com/glossary/desktop.html

Em 
     An em is a typographers unit of measurement that is proportioned to the
width of a capital letter "M." It will vary
     from font to font and will also vary with the point size of the font. 
En 
     An en is a typographers unit of measurement that is proportioned to the
width of a capital letter "N." It will vary from
     font to font and will also vary with the point size of the font. 
En Dash or Em Dash 
     A dash (hyphen) that will have its width equal to either the width of a
capital letter "N" or "M." 
En Space or Em Space 
     A space (between words) that will have its width equal to either the
width of a capital letter "N" or "M." 


http://www.protothought.com/glossary.htm

           Em: Unit of space (width) equal to the point size of the type.

           Em Dash: An em dash is used to abruptly change a thought within a
sentence or to connect
           two different thoughts within a sentence. The actual length of an
em dash is approximately
           four times the length of a hyphen and is relative to the set
width of the font which you are
           using. Em dashes received their name due to the fact that they
are equivalent to the width of
           the capital letter em (M). 
           Em Space: An Em space is a fixed amount of blank space equivalent
to the width of a capital
           letter em (M). Em spaces are frequently used for paragraph
indents and bullet item indents
           because they are fixed units. Em spaces are relative to the set
width of the font being used. 
           En Dash: An en dash is used to denote continuation; as in "pages
4-5" and "1966-1995." The
           actual length of an en dash is approximately two times the length
of a hyphen and is relative to
           the set width of the font which you are using. En dashes received
their name due to the fact
           that they are equivalent to the width of the capital letter en
(N). An en dash is one-half the
           width of an em dash. 
           En Space: An En space is a fixed amount of blank space equivalent
to the width of a capital
           letter en (N). En spaces are frequently used when a fixed amount
of space is needed, but less
           space than the more commonly used em space. En spaces are
relative to the set width of the
           font being used. An en space is one-half the width of an em
space. 

           Em dash: A punctuation mark generally used to signify a change or
interruption in the train of
           thought expressed in a sentence or to set off an explanatory
comment.

           En: Half an em.

           En dash: A punctuation mark used to indicate a range of dates or
numbers or to separate the
           elements of a compound adjective, one part of which is hyphenated
or consists of two words.


http://www.smus.bc.ca/depts/compstud/ds/glossary/glossary.htm

en Space 
     A space as wide as half the current point size (typically as wide as
the letter n in many fonts.) The related em space is
     as wide as the current point size (as wide as m in many fonts.) The en
dash is a dash as wide as an en space, and an em
     dash is a dash as wide as an em space. A no break space is as wide as a
regular space, but a web browser will not break
     the line at a no break space even if they would at a regular space. 


http://www.si-net.com/~cps/glosstest.html#GlossE

em 
     In composition, a unit of measurement exactly as wide and high as the
point size being set. So named because the
     letter "M" in early fonts was usually cast on a square body. 

en 
     In composition, one-half the width of an em. 


http://www.hypercorp.com/gain/pm/glossary.html#E
Em. In printing terms it is a square unit with edges equal in size to the
chosen point size. It gets its name from the letter M
which originally was as wide as the type size.

Em dash. A dash used in punctuation the length of one em. 

En dash. A dash approximately half the width of an em dash. 

En. A unit of measurement that is half as wide as an em. 


http://www.flexovendors.com/glossary.html#E
                      Em - In typesetting, a fixed space equal to the square
of the type size being used. One em (or
                      more) is often used as a standard of paragraph indent
in text.

                      En - A fixed space equal to one-half the width of an
em.


http://the-duke.duq-duke.duq.edu/notes/mpgd/week4/c006.htm

4.   Word spacing - spacing between words:    em
spacing is the phrase and measure unit and is the actual linear width of
the capital M in the particular type style.


http://www.fontsite.com/Pages/RulesOfType/ROT0997.html

An em is a unit of measure equal to the point size you are using. For
example, 
using 10-point type, an em dash would be approximately 10 points (approx. 
0.14 inches) wide, but this is dependent on the individual typeface.
Actually, 
this is probably the widest it would be. Many typefaces have em dashes that 
are slightly narrower than a full em, but still considerably wider than a
hyphen.

An en dash is typically half the length of an em dash (sometimes slightly
wider
than half, depending on the typeface) but still longer than a hyphen.


http://home2.swipnet.se/~w-20547/stylework/typograph1-en.html
has a paragraph on em quads, that sais that it is a square with sides as
long as the height of the font.


http://wwwdeanza.fhda.edu/GDCA/GD.online/Mgloss.html

     Em. The square of the body size of any type, used as a unit of measure.
In some expanded or condensed faces, the em is also expanded or condensed
from the square
     proportion.
     Em dash. A dash one em long. Also called a long dash.
     Em leader. Horizontal dots or dashes with one em between their centers.

     Em space. A space equal to the width of an em quad . 
     En. One-half of an em (see Em). 
     En dash. A dash one en long. Also called a short dash . 
     En leader. Horizontal dots or dashes with one en between their centers.

     En space. Space equal to the width of an en quad. 

http://w3c1.inria.fr/TR/PR-CSS2/fonts.html#font-descriptors

Certain values, such as width metrics, are expressed in units
that are relative to an abstract square whose height is the
intended distance between lines of type in the same type size.
This square is called the em square and it is the design grid on
which the glyph outlines are defined.


http://dtp-aus.com/typo/typterm.shtml

           Em 
                A unit of measurement exactly as wide and as high as the
body size of type being set. It is commonly
                used to measure spaces, indentions, column sizes, and pages,
and can be used for copyfitting and
                costing. A measurement of area, it is often confused with
the `Pica'. In 18-pt type the em is 18 points
                wide and 18 points high; in 12-pt type it is 12 points
square. 
           Em Dash 
                Also known as Em Rule. A dash centred on the x-height of
characters, one em long, used to indicate a
                pause in the sentence. 
           Em Space 
                A fixed amount of white space exactly one em wide, which
will not be `stretched' for justification
                purposes as will a space band. 
           En 
                A unit of measurement exactly one-half as wide as the body
size of type being set. In 18-pt type the en
                is 9 points wide and 18 points high; in 12-pt type it is 6
points wide and 12 points high. 
           En Dash 
                Also known as En rule. A dash centred on the x-height of
characters, one en long, used to indicate a
                range of values. 
           En Space 
                A fixed amount of white space exactly one en wide, which
will not be `stretched' for justification
                purposes as will a space band. 


http://www.ruddle.com/d-fonts.html

As you might guess, an "em" is the width of an old style capital "M" (no
points for guessing how wide an "en" is). But how
wide is an "em"? Well, a 10-point em dash (not to mention a 10-point "em
space") is 10 points high and 10 points wide. All
"en" things are half as wide (just five points wide in a 10-point font).

Actually, a 10-point capital em does not measure 10 points in height. If you
had a pica ruler (who doesn't?), you would find
it was just eight (or seven) points high. Why? Most serif (except modern)
and sans serif characters divide their vertical space
this way:


http://www.fontworks.co.jp/e/typography/talk/004.html
http://www.fontworks.co.jp/e/typography/talk/010.html


http://dv.go.dlr.de:8081/info/faqs/fonts/fonts-faq.2.html
       date, people realized that the inch was an archaic measure anyway;
       the point was set to be 1/12 of a pica, and an 83-pica distance
       was made equal to 35 centimeters. (Talk about arbitrary!)

So,
point =pica/12
83 pica = 35 cm

point=35/83/12 cm = 0.0351405622489959839357429718875 cm approx= 0.3514 mm
Q = 0.25 mm approx= 0.71 point  (from the jp site above)


http://www.concentric.net/~Brandt58/tframe2.html#em
   Em Space In linear measure, a distance equal to the type size, and in
   square measure, the square of the type size. Thus an em is 12 pt (or a 12
pt
   square) in 12 pt type. Also called mutton. 

   En Space Half an em. To avoid misunderstanding when instructions are
   given orally, typographers often speak of ems as muttons and ens as nuts.


http://www.howardprinting.com/glossary2.htm

          EM DASH
               An em dash is used to abruptly change a thought within a
sentence or to connect two
               different thoughts within a sentence. The actual length of an
em dash is approximately four
               times the length of a hyphen and is relative to the set width
of the font which you are using.
               Em dashes received their name due to the fact that they are
equivalent to the width of the
               capital letter em (M).

          EM SPACE
               An Em space is a fixed amount of blank space equivalent to
the width of a capital letter em
               (M). Em spaces are frequently used for paragraph indents and
bullet item indents because
               they are fixed units. Em spaces are relative to the set width
of the font being used.

          EN DASH
               An en dash is used to denote continuation; as in "pages 4-5"
and "1966-1995." The actual
               length of an en dash is approximately two times the length of
a hyphen and is relative to
               the set width of the font which you are using. En dashes
received their name due to the fact
               that they are equivalent to the width of the capital letter
en (N). An en dash is one-half the
               width of an em dash.

          EN SPACE
               An En space is a fixed amount of blank space equivalent to
the width of a capital letter en
               (N). En spaces are frequently used when a fixed amount of
space is needed, but less space
               than the more commonly used em space. En spaces are relative
to the set width of the font
               being used. An en space is one-half the width of an em space.


http://www-tradoc.monroe.army.mil/tpubs/regs/r25-30d.htm

em
  The square of the type size being used, so named
because the letter M was usually cast as metal type on a
square body. Thus, in 10-point type, an em is 10 points
wide and 10 points high.

em dash
  In typeset, a dash that is one em wide; in typescript,
two hyphens.

en
  One-half of an em.

en dash
  In typeset, a dash that is one en wide; in typescript, a
single hyphen.

http://bcarroll.siscom.net/upm/glossdfs.htm

Em Space 
     During the days of hot metal, the em space, as well as the en space and
thin space were actually non-printing blocks
     of metal used to add space between printed elements. An em space was
equal to the square of the point size being
     used, and most likely, it was equal to the width of the capital M. For
example, a 12-point em was 12 points high and
     12 points wide. In photo-typesetting, the em is generally typeface
sensitive, proportional to the design of the
     typeface. 

En Space 
     In both hot metal and photo-typesetting, the en space is equivalent to
half the width of an em space. 

http://www.hypermedic.com/style/fonts/fontglos.htm

Em 

     Originally the width of the letter "M" in a font size. In British type
setting practice it came to be formalized as a
     sixth of an inch. In the CSS specification, and this is the way we use
it in computing, an em is the height of the
     character cell of a particular size of font. 

     This means that for a given font size an em is the same size as the
font.e.g. When refering to a 36point font an
     em would be equal to half an inch. 

   Ex 

     Originally this refered to the width of the letter 'x'. In CSS practice
this is still the definition, and even if the
     font family does not have an 'x' character (e.g. a hebrew font), an x
height is still defined. 

     This measurement is important, because the apparent size of a font, as
opposed to its actual size is related to
     the height of the body, so that a 12 point 'Arial' font appears much
bigger than a 12 point 'Nuptial' font. An 'ex'
     s thus related to the apparent, as opposed to the actual size of the
font. 


http://www.fernhillpress.com/gloss-2.htm
em, em space, em quad 
     A common unit of measurement in typography. Em is traditionally defined
as the width of the uppercase M in the
     current face and point size. It is more properly defined as simply the
current point size. For example, in 12 point type,
     em is a distance of 12 points. 
em dash 
     A dash the length of an em is used to indicate a break in a sentence. 
en, en space, en quad 
     A common unit of measurement in typography. En is traditionally defined
as the width of the uppercase N in the
     current face and the current point size. It is more properly defined as
half the width of an em. 
en dash 
     A dash the length of an en is used to indicate a range of values. 


 http://www.waysidepress.com/desktop.htm

                  Em 

                                   An em is a typographers unit of
measurement that is
                                   proportioned to the width of a capital
letter "M." It will vary
                                   from font to font and will also vary with
the point size of the
                                   font. 
                  En 

                                        An en is a typographers unit of
measurement that is
                                   proportioned to the width of a capital
letter "N." It will vary
                                   from font to font and will also vary with
the point size of the
                                   font. 
                                        En Dash or Em Dash 

                                   A dash (hyphen) that will have its width
equal to
                                   either the width of a capital letter "N"
or "M." 
        En Space or Em Space 

                                        A space (between words) that will
have its width
                                   equal to either the width of a capital
letter "N" or
                                   "M." 


http://channels.microsoft.com/typography/glossary/ch6.htm

An em was so called because the letter M nearly always sat on a piece of
type metal
whose set (width) was the same as its size, giving a nearly square cross
section.
An en is half an em. Here again this was because the letter n usually sat on
a piece
of type whose set was half its size. Moreover, the average width of all
lower case
characters was an en. A w is wider than an n, but a , or i or l are all
narrower. 


http://microsoft.com/typography/OTSPEC/TTCH01.htm

                      In a TrueType font file point locations are described
in font units, or FUnits. An FUnit
                      is the smallest measurable unit in the em square, an
imaginary square that is used to size
                      and align glyphs. The dimensions of the em square
typically are those of the full body
                      height of a font plus some extra spacing to prevent
lines of text from colliding when
                      typeset without extra leading. 
Received on Thursday, 20 January 2000 15:12:01 GMT

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