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% $Header$

% Copyright 2003, 2004 by Till Tantau <tantau@users.sourceforge.net>.
%
% This program can be redistributed and/or modified under the terms
% of the GNU Public License, version 2.

\section{Guidelines for Creating Presentations}


\label{section-guidelines}

In this section I sketch the guidelines that I try to stick to when I
create presentations. These guidelines either arise out of experience,
out of common sense, or out of recommendations by other people or
books. These rules are certainly not intended as commandments that, if
not followed, will result in catastrophe. The central rule of
typography also applies to creating presentations: \emph{Every rule
  can be broken, but no rule may be ignored.} 




\subsection{Structuring a Presentation}

\label{section-structure-guidelines}



\subsubsection{Know the Time Constraints}

When you start to create a presentation, the very first thing you
should worry about is the amount of time you have for your
presentation. Depending on the occasion, this can
be anything between 2 minutes and two hours.

\begin{itemize}
\item
  A simple rule for the number of frames is that you should have at
  most one frame per minute.
\item
  In most situations, you will have less time for your presentation
  that you would like.
\item
  \emph{Do not try to squeeze more into a presentation than time
  allows for.} No matter how important some detail seems to you, it is
  better to leave it out, but get the main message across, than
  getting neither the main message nor the detail across.
\end{itemize}

In many situations, a quick appraisal of how much time you have will
show that you won't be able to mention certain details. Knowing this can
save you hours of work on preparing slides that you would have to remove
later anyway.



\subsubsection{Global Structure}

To create the ``global structure'' of a presentation, with the time
constraints in mind, proceed as follows:
\begin{itemize}
\item
  Make a mental inventory of the things you can reasonably talk about
  within the time available.
\item
  Categorize the inventory into sections and subsections.
\item
  For very long talks (like a 90 minute lecture), you might also
  divide your talk into independent parts (like a ``review of the
  previous lecture part'' and a ``main part'') using the |\part|
  command. Note that each  part has its own table of contents. 
\item
  Do not feel afraid to change the structure later on as you work on
  the talk.
\end{itemize}



\paragraph{Parts, Section, and Subsections.}

\begin{itemize}
\item
  Do not use more than four sections and not less than two per
  part.
\end{itemize}
Even four sections are usually too much, unless they follow 
a very easy pattern. Five and more sections are simply too hard to
remember for the audience. After all, when you present the table of
contents, the audience will not yet really be able to grasp the
importance and relevance of the different sections and will most
likely have forgotten them by the time you reach them.

\begin{itemize}
\item
  Ideally, a table of contents should be understandable by itself. In
  particular, it should be comprehensible \emph{before} someone has
  heard your talk.
\item
  Keep section and subsection titles self-explaining.
\item   
  Both the sections and the subsections should follow a logical
  pattern.
\item
  Begin with an explanation of what your talk is all about. (Do
  not assume that everyone knows this. The \emph{Ignorant Audience
  Law} states: Someone important in the audience always knows less
  than you think everyone should know, even if you take the Ignorant
  Audience Law into account.) 
\item
  Then explain what you or someone else has found out concerning the
  subject matter.
\item
  Always conclude your talk with a summary that repeats the main
  message of the talk in a short and simple way. People pay most
  attention at the beginning and at the end of talks. The summary is
  your ``second chance'' to get across a message.
\item
  You can also add an appendix part using the |\appendix| command. Put
  everything into this part that you do not actually intend to talk
  about, but that might come in handy when questions are asked.
\item
  Do not use subsubsections, they are evil.
\end{itemize}



\paragraph{Giving an Abstract}

In papers, the abstract gives a short summary of the whole paper in
about 100 words. This summary is intend to help readers appraise
whether they should read the whole paper or not.
\begin{itemize}
\item
  Since you audience is unlikely to flee after the first slide, in
  a presentation you usually do not need to present an abstract.
\item
  However, if you can give a nice, succinct statement of your
  talk, you might wish to include an abstract.
\item  
  If you include an abstract, be sure that it is \emph{not} some long 
  text but just a very short message.
\item
  \emph{Never, ever} reuse a paper abstract for a presentation,
  \emph{except} if the abstract is ``We show $\operatorname{P} =
  \operatorname{NP}$'' or ``We show $\operatorname{P} \neq
  \operatorname{NP}$''
\item
  If your abstract is one of the above two, double-check whether
  your proof is correct.
\end{itemize}





\paragraph{Numbered Theorems and Definitions.}

A common way of globally structuring (math) articles and books is to
use consecutively numbered definitions and theorems. Unfortunately,
for presentations the situation is a bit more complicated and I would
like to discourage using numbered theorems in presentations. The
audience has no chance of remembering these numbers. \emph{Never} say
things like ``now, by Theorem~2.5 that I showed you earlier, we have
\dots'' It would be much better to refer to, say, Kummer's Theorem
instead of Theorem~2.5. If Theorem~2.5 is some obscure theorem that
does not have its own name (unlike Kummer's Theorem or Main Theorem or
Second Main Theorem or Key Lemma), then the audience will have
forgotten about it anyway by the time you refer to it again.

In my opinion, the only situation in which numbered theorems make
sense in a presentation is in a lecture, in which the students can read
lecture notes in parallel to the lecture where the theorems are
numbered in exactly the same way.

If you do number theorems and definition, number everything
consecutively. Thus if there are one theorem, one lemma, 
and one definition, you would have Theorem~1, Lemma~2, and
Definition~3. Some people prefer all three to be numbered~1. I would
\emph{strongly} like to discourage this. The problem is that this
makes it virtually impossible to find anything since Theorem~2 might
come after Definition~10 or the other way round. Papers and, worse,
books that have a Theorem~1 and a Definition~1 are a pain.
\begin{itemize}
\item
  Do not inflict pain on other people.
\end{itemize}


\paragraph{Bibliographies.}

You may also wish to present a bibliography at the end of your talk,
so that people can see what kind of ``further reading'' is possible. 
When adding a bibliography to a presentation, keep the following in mind:

\begin{itemize}
\item
  It is a bad idea to present a long bibliography in a 
  presentation. Present only very few references. (Naturally, this
  applies only to the talk itself, not to a possible handout.)
\item
  If you present more references than fit on a single slide you can be 
  almost sure that none of them will not be remembered. 
\item
  Present references only if they are intended as ``further reading.''
  Do not present a list of all things you used like in a paper.
\item
  You should not present a long list of all your other great papers
  \emph{except} if you are giving an application talk.
\item
  Using the |\cite| commands can be confusing since the audience
  has little chance of remembering the citations. If you cite the
  references, always cite them with full author name and year like
  ``[Tantau, 2003]'' instead of something like ``[2,4]'' or
  ``[Tan01,NT02]''.
\item
  If you want to be modest, you can abbreviate your name when citing
  yourself as in ``[Nickelsen and T., 2003]'' or ``[Nickelsen and T,
  2003]''. However, this can be confusing for the audience since it is
  often not immediately clear who exactly ``T.'' might be. I recommend
  using the full name.
\end{itemize}




\subsubsection{Frame Structure}

\label{section-frame-guidelines}
\label{section-guidelines-local}

Just like your whole presentation, each frame should also be
structured. A frame that is solely filled with some long text is very
hard to follow. It is your job to structure the contents of each frame
such that, ideally, the audience immediately seems which information
is important, which information is just a detail, how the presented
information is related, and so on.



\paragraph{The Frame Title}

\begin{itemize}
\item
  Put a title on each frame. The title explains the contents of the
  frame to people who did not follow all details on the slide.
\item
  The title should really \emph{explain} things, not just give a
  cryptic summary that cannot be understood unless one has understood
  the whole slide. For example, a title like ``The Poset'' will have
  everyone puzzled what this slide might be about. Titles like
  ``Review of the Definition of Partially Ordered Sets (Posets)'' or
  ``A Partial Ordering on the Columns of the Genotype Matrix'' are
  \emph{much} more informative.
\item
  Ideally, titles on consecutive frames should ``tell a story'' all by
  themselves.
\item
  In English, you should \emph{either} \emph{always} capitalize all words in
  a frame title except for words like ``a'' or ``the'' (as in a
  title), \emph{or} you \emph{always} use the normal lowercase
  letters. Do \emph{not} mix this; stick to one rule. The same is true
  for block titles. For example, do not use titles like ``A short
  Review of Turing machines.'' Either use ``A Short Review of Turing
  Machines.'' or ``A short review of Turing machines.'' (Turing is
  still spelled with a capital letter since it is a name).
\item
  In English, the title of the whole document should be
  capitalized, regardless of whether you capitalize anything else.
\item
  In German and other languages that have lots of capitalized words,
  always use the correct upper-/lowercase letters. Never capitalize
  anything in addition to what is usually capitalized.
\end{itemize}



\paragraph{How Much Can I Put On a Frame?}

\begin{itemize}
\item
  A frame with too little on it is better than a frame with too much
  on it. A usual frame should have between 20 and 40 words. The
  maximum should be at about 80 words.
\item
  Do not assume that everyone in the audience is an expert on the
  subject matter. Even if the
  people listening to you should be experts, they may last have heard
  about things you consider obvious several years ago. You should
  always have the time for a quick reminder of what exactly a
  ``semantical complexity class'' or an ``$\omega$-complete partial
  ordering'' is.
\item
  Never put anything on a slide that you are not going to explain
  during the talk, not even to impress anyone with how
    complicated your subject matter really is. However, you may
  explain things that are not on a slide.
\item
  Keep it simple. Typically, your audience will see a slide for less
  than 50 seconds. They will not have the time to puzzle through long
  sentences or complicated formulas.
\item
  Lance Forthnow claims: PowerPoint users give better talks. His
  reason: Since PowerPoint is so bad at typesetting math, they use
  less math, making their talks easier to understand.

  There is some truth in this in my opinion. The great
  math-typesetting capabilities of \TeX\ can easily lure you into
  using many more formulas than is necessary and healthy. For example,
  instead of writing {\catcode `|=12``Since $\left|\{x \in \{0,1\}^*
  \mid x \sqsubseteq y\}\right| < \infty$}, we have\dots''\ use ``Since
  $y$ has only finitely many prefixes, we have\dots''

  You will be surprised how much mathematical text can be reformulated
  in plain English or can just be omitted. Naturally, if some
  mathematical argument is what you are actually talking about, as in
  a math lecture, make use of \TeX's typesetting capabilities to your
  heart's content. 
\end{itemize}



\paragraph{Structuring a Frame}

\begin{itemize}
\item
  Use block environments like |block|, |theorem|, |proof|, |example|,
  and so on.
\item
  Prefer enumerations and itemize environments over plain text.
\item
  Use |description| when you define several things.
\item
  Do not use more than two levels of ``subitemizing.'' \beamer\
  supports three levels, but you should not use that third
  level. Mostly, you should not even use the second one. Use good
  graphics instead.
\item
  Do not create endless |itemize| or |enumerate| lists.
\item
  Do not uncover lists piecewise. 
\item
  Emphasis is an important part of creating structure. Use |\alert| to
  highlight important things. This can be a single word or a whole
  sentence. However, do not overuse hilighting since this will negate
  the effect.
\item
  Use columns.
\item
  \emph{Never} use footnotes. They needlessly disrupt the flow of
  reading. Either what is said in the footnote is important and should
  be put in the normal text; or it is not important and should be
  omitted (\emph{especially} in a presentation).
\item
  Use |quote| or |quotation| to typeset quoted text.
\item
  Do not use the option |allowframebreaks| except for long
  bibliographies.
\item
  Do not use long bibliographies.
\end{itemize}




\paragraph{Writing the Text}

\begin{itemize}
\item
  Use short sentences.
\item
  Prefer phrases over complete sentences. For example,
  instead of ``The figure on the left shows a Turing machine, the
  figure on the right shows a finite automaton.''\ try ``Left: A Turing
  machine. Right: A finite automaton.'' Even better, turn this into an
  itemize or a description.
\item
  Punctuate correctly: no punctuation after phrases, complete
  punctuation in and after complete sentences.
\item
  \emph{Never} use a smaller font size to ``fit more on a frame.''
  \emph{Never ever} use the \emph{evil} option |shrink|.
\item
  Do not hyphenate words. If absolutely necessary, hyphenate words
  ``by hand,'' using the command~|\-|.
\item
  Break lines ``by hand'' using the command~|\\|. Do not rely on
  automatic line breaking. Break where there is a logical pause. For 
  example, good breaks in ``the tape alphabet is larger
  than the input alphabet'' are before ``is'' and before the second
  ``the.'' Bad breaks are before either ``alphabet'' and before
  ``larger.''
\item
  Text and numbers in figures should have the \emph{same} size as
  normal text. Illegible numbers on axes usually ruin a chart and its
  message.
\end{itemize}




\subsubsection{Interactive Elements}

Ideally, during a presentation you would like to present your
slides in a perfectly linear fashion, presumably by pressing the
page-down-key once for each slide. However, there are different
reasons why you might have to deviate from this linear order:
\begin{itemize}
\item
  Your presentation may contain ``different levels of detail'' that
  may or may not be skipped or expanded, depending on the audience's
  reaction.
\item
  You are asked questions and wish to show supplementary slides.
\item
  You present a complicated picture and you have to ``zoom out''
  different parts to explain details.
\item
  You are asked questions about an earlier slide, which forces you to 
  find and then jump to that slide.
\end{itemize}
You cannot really prepare against the last kind of questions. In this
case, you can use the navigation bars and symbols to find the slide
you are interested in, see \ref{section-navigation-bars}.

Concerning the first three kinds of deviations, there are several
things you can do to prepare ``planned detours'' or ``planned
short cuts''.
\begin{itemize}
\item
  You can add ``skip buttons.'' When such a button
  is pressed, you jump over a well-defined part of your talk. Skip
  button have two advantages over just pressing the forward key
  is rapid succession: first, you immediately end up at the correct
  position and, second, the button's label can give the audience a
  visual feedback of what exactly will be skipped. For example, when
  you press a skip button labeled ``Skip proof'' nobody will start
  puzzling over what he or she has missed.
\item
  You can add an appendix to your talk. The appendix is kept
  ``perfectly separated'' from the main talk. Only once you ``enter''
  the appendix part (presumably by hyperjumping into it), does the
  appendix structure become visible. You can put all frames that you
  do not intend to show during the normal course of your talk, but
  which you would like to have handy in case someone asks, into this
  appendix.
\item
  You can add ``goto buttons'' and ``return buttons'' to create
  detours. Pressing a goto button will jump to a certain part of the
  presentation where extra details can be shown. In this part, there
  is a return button present on each slide that will jump back to the
  place where the goto button was pressed.
\item
  In \beamer, you can use the |\againframe| command to ``continue''
  frames that you previously started somewhere, but where certain
  details have been suppressed. You can use the |\againframe| command
  at a much later point, for example only in the appendix to show
  additional slides there.
\item
  In \beamer, you can use the |\framezoom| command to create links to
  zoomed out parts of a complicated slide.
\end{itemize}





\subsection{Using Graphics}

Graphics often convey concepts or ideas much more efficiently than
text: A picture can say more than a thousand words. (Although,
sometimes a word can say more than a thousand pictures.) 

\begin{itemize}
\item
  Put (at least) one graphic on each slide, whenever
  possible. Visualizations help an audience enormously.
\item
  Usually, place graphics to the left of the text. (Use the
  |columns| environment.) In a left-to-right reading culture, we look
  at the left first.
\item
  Graphics should have the same typographic parameters as the
  text: Use the same fonts (at the same size) in graphics as in the
  main text. A small dot in a graphic should have exactly the same 
  size as a small dot in a text. The line width should be the same as
  the stroke width used in creating the glyphs of the font. For
  example, an 11pt non-bold Computer Modern font has a stroke width of
  0.4pt.
\item
  While bitmap graphics, like photos, can be much more colorful than the
  rest of the text, vector graphics should follow the same ``color
  logic'' as the main text (like black~= normal lines, red~= hilighted
  parts, green~= examples, blue~= structure).
\item
  Like text, you should explain everything that is shown on a
  graphic. Unexplained details make the audience puzzle whether this
  was something important that they have missed. Be careful when
  importing graphics from a paper or some other source. They usually
  have much more detail than you will be able to explain and should be
  radically simplified.
\item
  Sometimes the complexity of a graphic is intensional and you
  are willing to spend much time explaining the graphic in great
  detail. In this case, you will often run into the problem that fine
  details of the graphic are hard to discern for the audience. In this
  case you should use a command like |\framezoom| to create
  anticipated zoomings of interesting parts of the graphic, see
  Section~\ref{section-zooming}. 
\end{itemize}



\subsection{Using Animations and Transitions}

\begin{itemize}
\item
  Use animations to explain the dynamics of systems, algorithms, etc.
\item
  Do \emph{not} use animations just to attract the attention of your
  audience. This often distracts attention away from the main topic of the
  slide. No matter how cute a rotating,
  flying theorem seems to look and no matter how badly you feel your
  audience needs some action to keep it happy, most people in the
  audience will typically feel you are making fun of them. 
\item
  Do \emph{not} use distracting special effects like ``dissolving''
  slides unless you have a very good reason for using them. If you use
  them, use them sparsely. 
  They \emph{can} be useful in some situations: For example, you might
  show a   young boy on a slide and might wish to dissolve this slide
  into   slide showing a grown man instead. In this case, the
  dissolving  gives the audience visual feedback that the young boy
  ``slowly becomes'' the man. 
\end{itemize}




\subsection{Choosing Appropriate Themes}

\beamer\ comes with a number of different themes. When choosing a
theme, keep the following in mind:

\begin{itemize}
\item
  Different themes are appropriate for different occasions. Do not
  become too attached to a favorite theme; choose a 
  theme according to occasion.
\item
  A longer talk is more likely to require navigational hints
  than a short one. When you give a 90 minute lecture to students, you
  should choose a theme that always shows a sidebar with the current
  topic hilighted so that everyone always knows exactly what's the
  current ``status'' of your talk is; when you give a ten-minute
  introductory speech, a table of contents is likely to just seem
  silly.
\item
  A theme showing the author's name and affiliation is appropriate in
  situation where the audience is likely not to know you (like during
  a conference). If everyone knows you, having your name on each slide
  is just vanity. 
\item
  First choose a presentation theme that has a layout that is
  appropriate for your talk.
\item
  Next you might wish to change the colors by installing a different
  color theme. This can drastically change the appearance of your
  presentation. A ``colorful'' theme like |Berkeley| will look much
  less flashy if you use the color themes |seahorse| and |lily|. 
\item
  You might also wish to change the fonts by installing a different
  font theme.
\end{itemize}



\subsection{Choosing Appropriate Colors}

\begin{itemize}
\item
  Use colors sparsely. The prepared themes are already quite
  colorful (blue~= structure, red~= alert, green~= example). If you
  add more colors for things like code, math text, etc., you should
  have a \emph{very} good reason. 
\item
  Be careful when using bright colors on white background,
  \emph{especially} when using green. What looks good on your monitor
  may look bad during a presentation due to the different ways
  monitors, beamers, and printers reproduce colors. Add lots of black
  to pure colors when you use them on bright backgrounds.
\item
  Maximize contrast. Normal text should be black on white or at least
  something very dark on something very bright. \emph{Never} do things
  like ``light green text on not-so-light green background.''
\item
  Background shadings decrease the legibility without increasing the
  information content. Do not add a background shading just because it
  ``somehow looks nicer.'' 
\item
  Inverse video (bright text on dark background) can be a problem
  during presentations in bright environments since only a small
  percentage of the presentation area is light up by the
  beamer. Inverse video is harder to reproduce on printouts and on
  transparencies. 
\end{itemize}






\subsection{Choosing Appropriate Fonts and Font Attributes}

Text and fonts literally surround us constantly. Try to think of the
last time when  there was no text around you within ten
meters. Likely, this has never happened in your life! 
(Whenever you wear clothing, even a swim suit, there is a lot of text
right next to your body.) The history of fonts is nearly as long as
the history of civilization itself. There are tens of thousands of fonts
available these days, some of which are the product of hundreds of
years of optimization.

Choosing the right fonts for a presentation is by no means
trivial and wrong choices will either just ``look bad'' or, worse,
make the audience having trouble reading your slides.
This user's guide cannot replace a good book on typography, but in the
present section you'll find several hints that should help you setup 
fonts for a \beamer\ presentation that look good.
A font has numerous attributes like weight, family, or size. All of
these have an impact on the usability of the font in
presentations. In the following, these attributes are described and
advantages and disadvantages of the different choices are sketched.


\subsubsection{Font Size}

\label{section-sizes}

Perhaps the most obvious attribute of a font is its size. Fonts are
traditionally measured in ``points.'' How much a point is depends on
whom you ask. \TeX\ thinks a point is the 72.27th part of an inch,
which is 2.54 cm. On the other hand, PostScript and Adobe think a
point is the 72th part of an inch (\TeX\ calls this a big point). The
are differences between American and European points. Once it is
settled how much a point is, claiming that a text is in ``11pt'' means
that the ``height'' of the letters in the font are 11pt. However, this
``height'' stems from the time when letters where still cast in lead
and refers to the the vertical size of the lead letters. It thus does
not need to have any correlation with the actual height of, say, the
letter x or even the letter M. The letter x of an 11pt Times from
Adobe will have a height that is different from the height of the
letter x of an 11pt Times from UTC and the letter x of an 11pt
Helvetica from Adobe will have yet another height.

Summing up, the font size has little to do with the actual size of
letters. Rather, these days it is a convention that 10pt or 11pt is
the size a font should be printed for ``normal reading.'' Fonts are
designed so that they can optimally be read at these sizes.

In a presentation the classical font sizes obviously loose their
meaning. Nobody could read a projected text if it were actually
11pt. Instead, the projected letters need to be several centimeters
high. Thus, it does not really make sense to specify ``font sizes''
for presentations in the usual way. Instead, you should try to think
of the number of lines that will fit on a slide if you were to fill
the whole slide with line-by-line text (you are never going to do that
in practice, though). Depending on how far your audience is removed
from the projection and on how large the projection is, between 10 and
20 lines should fit on each slide. The less lines, the more readable
your text will be.

In \beamer, the default sizes of the fonts are chosen in a way that
makes it difficult to fit ``too much'' onto a slide. Also, it will
ensure that your slides are readable even under bad conditions like a
large room and a small only a small projection area. However, you may
wish to enlarge or shrink the fonts a bit if you know this to be more
appropriate in your presentation environment.

Once the size of the normal text is settled, all other sizes are
usually defined relative to that size. For this reason, \LaTeX\ has 
commands like |\large| or |\small|. The actual size these commands
select depends on the size of normal text.

In a presentation, you will want to use a very small font for text in
headlines, footlines, or sidebars since the text shown there is not
vital and is read at the audience's leasure. Naturally, the text should
still be large enough that it actually \emph{can} be read without
binoculars. However, in a normal presentation environment the audience
will still be able to read even |\tiny| text when necessary.

However, using small fonts can be tricky. Many PostScript fonts are
just scaled down when used at small sizes. When a font is
used at less than its normal size, the characters should actually be
stroked using a slightly thicker ``pen'' than the one resulting from
just scaling things. For this reason, high quality 
multiple master fonts or the Computer Modern fonts use different
fonts for small characters and for normal characters. However, when
you use a normal Helvetica or Times font, the characters are just
scaled down. A similar problem arises when you use a light font on a
dark background. Even when printed on paper in high resolution,
light-on-dark text tends to be ``overflooded'' by the dark
background. When light-on-dark text is rendered in a presentation this
effect can be much worse, making the text almost impossible to read.

You can counter both negative effects by using a bold versions for
small text.

In the other direction, you can use larger text for titles. However,
using a larger font does not always have the desired effect. Just
because a frame title is printed in large letters does not
mean that it is read first. Indeed, have a look at the cover of your
favorite magazine. Most likely, the magazine's name is the typeset in the
largest font, but you your attention will nevertheless first go to the
topics advertised on the cover. Likewise, in the table of contents you
are likely to first focus on the entries, not on the words ``Table of
Contents.'' Most likely, you would not spot a spelling mistake there
(a friend of mine actually managed to misspell \emph{his own name} on
the cover of his master's thesis and nobody noticed until a year
later). In essence, large text at the top of a page signals
``unimportant since I know what to expect.'' So, instead of using a
very large frame title, also consider using a normal size frame title
that is typeset in bold or in italics. 





\subsubsection{Font Families}

\label{section-guidelines-serif}

The other central property of any font is its family. Examples of font
families are Times or Helvetica or Futura. As the name suggests, a lot
of different fonts can belong to the same family. For example, Times
comes in different sizes, there is a bold version of Times, an
italics version, and so on. To confuse matters, font families like
Times are often just called the ``font Times.''

The are two large classes of font families: serif fonts and
sans-serif fonts. A sans-serif font is a font in
which the letters do not have serifs (from French \emph{sans}, which
means ``without''). Serifs are the little hooks at the ending of the
strokes that make up a letter. The font you are currently reading is a
serif font. \textsf{By comparison, this text is in a sans-serif font.}
Sans-serif fonts are (generally considered to be) easier to read
when used in a presentation. In low resolution rendering, serifs
decrease the legibility of a font. However, on projectors with very
high resolution serif text is just as readable as sans-serif text. A
presentation typeset in a serif font creates a more conservative
impression, which might be exactly what you wish to create. 

Most likely, you'll have a lot of different font families preinstalled
on you system. The default font used by \TeX\ (and \beamer) is the
Computer Modern font. It  is the original font family designed by Donald
Knuth himself for the \TeX\ program. It is a mature font that comes
with just about everything you could wish for: extensive mathematical
alphabets, outline PostScript versions, real small caps, real oldstyle
numbers, specially designed small and large letters, and so on.

However, there are reasons for using font families other than Computer
Modern: 
\begin{itemize}
\item
  The Computer Modern fonts are a bit boring if you have seen them too
  often. Using another font (but not Times!) can give a fresh look.
\item
  Other fonts, especially Times and Helvetica, are sometime rendered
  better since they seem to have better internal hinting.
\item
  The sans-serif version of Computer Modern is not nearly as
  well-designed as the serif version. Indeed, the sans-serif version
  is, in essence, the serif version with different design parameters,
  not an independent design.
\item
  Computer modern needs much more space than more economic fonts like
  Times (this explains why Times is so popular with people who need
  to squeeze their great paper into just twelve pages). To be fair,
  Times was specifically designed to be economic (the newspaper
  company publishing The Times needed robust, but space-economic font).
\end{itemize}

A small selection of alternatives to Computer Modern:
\begin{itemize}
\item
  Helvetica is an often used alternative. However, Helvetica also
  tends to look boring (since we see it everywhere) and it has a very
  large x-height (the height of the letter~x in comparison to a letter
  like~M). A large x-height is usually considered good for languages
  (like English) that use uppercase letters seldomly and not-so-good
  for languages (like German) that use uppercase letters a lot. (I
  have never been quite convinced by the argument for this, though.)
  Be warned: the x-height of Helvetica is so different from the
  x-height of Times that mixing the two in a single line looks
  strange. The packages for loading Times and Helvetica provide
  options for fixing this, though.
\item
  Futura is, in my opinion, a beautiful font that is very well-suited
  for presentations. Its thick letters make it robust against
  scaling, inversion, and low contrast. Unfortunately, while it is
  most likely installed on your system somewhere in some form, getting
  \TeX\ to work with it is a complicated process.
\item
  Times is a possible alternative to Computer Modern. Its main
  disadvantage is that it is a serif font, which requires a
  high-resolution projector. Naturally, it also used very often, so we
  all know it very well.
\end{itemize}

Families that you should \emph{not} use for normal text include:
\begin{itemize}
\item
  All monospaced fonts (like Courier).
\item
  Script fonts (which look like handwriting). Their stroke width is
  way too small for a presentation.
\item
  More delicate serif fonts like Stempel and possibly even Garamond
  (though Garamond is really a beautiful font for books).
\item
  Gothic fonts. Only a small fraction of your audience will be able to
  read them fluently. 
\end{itemize}

There is one popular font that is a bit special: Microsoft's Comic
Sans. On the one hand, there is a website lobbying for banning the use
of this font. Indeed, the main trouble with the font is that it is not
particularly well-readable and that math typeset partly using this
font looks terrible. On the other hand, this font \emph{does} create
the impression of a slide ``written by hand,'' which gives the
presentation a natural look. Think twice before using this font, but
do not let yourself be intimidated.

One of the most important rules of typography is that you should use
as little fonts as possible in a text. In particular, typographic
wisdom dictates that you should not use more than two different
families on one page. However, when typesetting
mathematical text, it is often necessary and useful to use different
font families. For example, it used to be common practice to use
Gothic letters do denote vectors. Also, program texts are often
typeset in monospace fonts. If your audience is used to a certain font
family for a certain type of text, use that family, regardless of what
typographic wisdom says.

A common practice in typography is to use a sans serif fonts for
titles and serif fonts for normal text (check your favorite
magazine). You can \emph{also} use two different sans serif fonts or
two different serif fonts, but you then have to make sure that the
fonts look ``sufficiently different.'' If they look only slightly
different, the page will look ``somehow strange,'' but the audience
will not be able to tell why. For example, do not mix Arial and
Helvetica (they are almost identical) or Computer Modern and
Baskerville (they are quite similar). A combination of Gills Sans and
Helvetica is dangerous but perhaps possible. A combination like Futura
and Optima is certainly ok, at least with respect to the fonts being
very different.




\subsubsection{Font Shapes: Italics and Small Capitals}

\label{section-italics}
\label{section-smallcaps}

\LaTeX\ introduces the concept of the \emph{shape} of a font. The only
really important ones are italic and small caps.
An \emph{italic} font is a font in which the text is slightly slanted
to the right \emph{like this}. Things to know about
italics:
\begin{itemize}
\item
  Italics are commonly used in novels to express emphasis. However,
  especially with sans-serif fonts, italics are typically not ``strong
  enough'' and the emphasis gets lost in a presentation. Using a
  different color or bold text seems better suited for presentations
  to create emphasis. 
\item
  If you look closely, you will notice that italic text is not only
  slanted but that different letters are actually used (compare a and
  \emph{a}, for example). However, this is only true for serif text,
  not for sans-serif text. Text that is only slanted without using
  different characters is called  ``slanted'' instead of ``italic.''
  Sometimes, the word ``oblique'' is also used for slanted, but it
  sometimes also used for italics, so it is perhaps best to avoid
  it. Using slanted serif text is very much frowned upon by
  typographers and is considered ``cheap computer typography.''
  However, people who use slanted text in their books include Donald
  Knuth.

  In a presentation, if you go into the trouble of using a serif font
  for some part of it, you should also use italics, not slanted text.
\item
  The different characters used for serif italics have changed much
  less  from the original handwritten letters they are based on than
  normal serif text. For this reason, serif italics creates the
  impression of handwritten text, which may be desirable to give a
  presentation a more ``personal touch'' (although you can't get very
  personal using Times italics, which everyone has seen a thousand
  times). However, it is harder to read than normal text, so do not
  use it for text more than a line long.
\end{itemize}

The second font shape supported by \TeX\ are small capital
letters. Using them can create a conservative, even formal
impression, but some words of caution:

\begin{itemize}
\item
  Small capitals are different from all-uppercase text. A small caps
  text leaves normal uppercase letters unchanged and uses smaller
  versions of the uppercase letters for normal typesetting lowercase
  letters. Thus the word ``German'' is typeset as \textsc{German}
  using small caps, but as \uppercase{German} using all uppercase
  letters.
\item
  Small caps either come as ``faked'' small caps or as ``real''
  small caps. Faked small caps are created by just scaling down
  normal uppercase letters. This leads to letters the look too
  thin. Real small caps are specially designed smaller versions of
  the uppercase letters that have the same stroke width as normal
  text.
\item
  Computer Modern fonts and expert version of PostScript fonts come
  with real small caps (though the small caps of Computer Modern are
  one point size too large for some unfathomable reason---but your
  audience is going to pardon this since it will not notice
  anyway). ``Simple'' PostScript fonts like out-of-the-box Helvetica
  or Times only come with faked small caps.
\item
  Text typeset in small caps is harder to read than normal text. The
  reason is that we read by seeing the ``shape'' of words. For
  example, the word ``shape'' is mainly recognized by seing one
  normal letter, one ascending letter, a normal letter, one
  descending letter, and a normal letter. One has much more trouble
  spotting a misspelling like ``shepe''  than ``spape''. Small caps
  destroy the shape of words since \textsc{shape}, \textsc{shepe}
  and \textsc{spape} all have the same shape, thus making it much
  harder to tell them apart. Your audience will read small caps more
  slowly than normal text. This is, by the way, why legal
  disclaimers are often written in uppercase letters: not to make
  them appear more important to you, but to make them much harder to
  actually read.
\end{itemize}



\subsubsection{Font Weight}

The ``weight'' of a font refers to the thickness of the
letters. Usually, fonts come as regular or as bold fonts. There often
also exist semibold, ultrabold (or black), thin, or ultrathin (or hair)
versions.

In typography, using a bold font to create emphasis, especially within
normal text, is frowned upon (bold words in the middle of a normal
text are referred to as ``dirt''). For presentations this rule of not
using bold text does not really apply. On a presentation slide there
is usually very little text and there are numerous elements that try
to attract the viewer's attention. Using the traditional italics to
create emphasis will often be overlooked. So, using bold text, seems a
good alternative in a presentation. However, an even better
alternative is using a bright color like red to attract attention.

As pointed out earlier, you should use bold text for small text
unless you use an especially robust font like Futura.



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