MasterView International
by Luigi Canali De Rossi
July 15th, 2002
One of the most frequent questions I get during my courses deals with
legibility. I usually warn my students about being concerned first about
readability issues, and give them some generic guidelines. But I have
realized that they want the precise rules, they want something scientific
to be applied as a rule which works for all situations.
>From here the need to write an article for MasterView where I give
you all these rules.
Here we go.
My first suggestion is to be careful about the use of the right fonts.
I always explain to them the difference between Serif and Sans Serif fonts
(see MasterView Issue #8, art. 1).
On this matter there is something more: the rule of the X-height.
You probably have noticed that some fonts may have the same point size
(e.g. both 12 points) but have a smaller X-height. The X-height is the
product of the number of lowercase letters (such as "a",
"e", "c" and so on) for the physical height of those lowercase letters.
I explain: Arial or Helvetica, for instance, have a greater X-height
than Garamond or Times New Roman, so the latter will be less readable at
the same size. In this case, you are recommended to increase the font size
of those fonts which have a lower X-height.
For what it concerns how to improve readability, please have a look at:
MasterView Issue #8, art. 2.
MasterView Issue #8, art. 5.
In those articles you will find interesting tips and basic rules to
apply to your text.
To end with what people like the most, a scientific rule about font size
compared to screen size and projector room size.
This rule is called "8H" rule. It states that, calling H the
height of the projector screen, the maximum distance of your last viewer
in the audience should be 8H, that is 8 times the screen height. Meeting
this requirement, and assuming that the image projector is the best
possible, the room light is good (not too dark) and the average viewer has no
viewing handicaps, you will
be sure that the ones who sit in the last rows will be able to easily read
your text.
But the rule says something more: so far, you have set the right
distance between the screen and the last rows. Now you have to deal with
font size within the screen.
Considering the height of the PowerPoint slide show you can safely
choose a font size that is not smaller than 1/25 of it. How can I make it
easier? I will explain it to you step by step with also some examples.
1) Calculate the height of the slides
2) Keep in mind that each centimeter corresponds, approximately, to
28.25 points
3) Multiply the height of your screen in centimeters for 28.25 points
and you will obtain the height in points
4) Divide the height in points by 25 and you will have found exactly
the minimum size, in points, of your fonts.
An example?
a) To determine the slide's height, go to "File" >>
"Page setup..." and you will see that the standard height for an
"on-screen show" is 19.05 cm
b) Multiply the height (19.05 cm) for 28.25 points (obtaining almost
540 points)
c) Divide 540 points by 25 and you will obtain almost 22, that is the
minimum size (in points) to use for your presentation
In inches, a typical PowerPoint slide is 7.5 inches, so it results that
an inch is approximately 72 points.
Going back to our "8H" rule, and having set that:
1) the maximum distance between the screen and the last viewer is given
by 8 times the height of the screen
2) the minimum readable font size is given by the height of the
PowerPoint slide divided by 25
we can conclude that a 22-point font size will be readable by an
audience which is not farther than 8 times the height of the projector
screen.
Thus, in case you notice that the projector screen is at a greater
distance from the last row, you should increase the font size to
compensate this. For instance, if the last row is at 16 meters from the
screen which is only 1 meter tall (the maximum distance should be 8
meters), you should double the font size in your presentation.
The last trick comes from PowerPoint. There are some rules you can set
about minimum font size which will help you not to use smaller fonts.
Click on "Tools" >> "Options" and click in
the "Spelling and Style" tab. Now, click on "Style Options" and then click on the "Visual Clarity" tab.
Here you can set some rules such as the minimum title and body text
size, the number of bullets per slide and the number of lines per bullets.
Check it out, it will perform these tasks automatically.
You can read this article in the original issue of MasterView.
