Enlarged font size

Not all visually impaired people use technical aids to navigate the Internet more easily. The ability to enlarge the font is an important element in ensuring that the website information can be read by all visitors. However, people with good eyesight also need to enlarge the font in certain situations. At the same time, more and more elderly people are surfing the net; they too depend on being able to enlarge the text. In this context, it is important to define font sizes not in pixels, but as a percentage or "em"

To increase font size, "toolboxes" (usually with JavaScript) are implemented, some of which are specific to the user. These allow the visitor to change the text size by clicking on the symbols. We advise against this type of font enlargement for the following reasons:

• On a second visit, if no cookie has been set, the visitor must click on the symbol to enlarge the text again. This step is not necessary if the automated browser functions are used. Here the user can set the font size display in his browser once according to his needs and does not have to worry about the font size for each individual website.
• In most cases, such additional toolboxes are realised with Java-Script, which in turn requires that the website visitors have not deactivated this function.

Note: Modern browsers can enlarge the fonts even when the information is fixed, but the website must be prepared for this case.

Source and further information:
"Prioritizing Web Usability" von Jakob Nielsen/Hoa Loranger,
sowie die Tipps des W3C: 
www.w3.org/2003/07/30-font-size
www.bitvtest.de/infothek/artikel/lesen/wcag2-schriftgroesse-skalierbarkeit.html