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Principle: Text that must be read should have high contrast

Favor black text on white or pale yellow backgrounds. Avoid gray backgrounds.

Principle: Use font sizes that are large enough to be readable on standard displays

You must demand of your marketing people that they tell you what the expected range of your customer’s standard displays will be. You then need to work with your graphic design and engineering people to ensure that your code will show up in appropriate sizes across that range of displays. It need not be one-size-fits-all. For example, CSS can mold itself to the system in which it finds itself.

Principle: Favor particularly large characters for the actual data you intend to display, as opposed to labels and instructions.

For example, the label, “Last Name,” can afford to be somewhat small. Habitual users will learn that that two-word gray blob says “Last Name.” Even new users, based on the context of the form on which it appears, will have a pretty good guess that it says “Last Name.” The actual last name entered/displayed, however, must be clearly readable. This becomes even more important for numbers. Human languages are highly redundant, enabling people to “heal” garbled messages. Numbers, however, unless they follow a very strict protocol, have no redundancy, so people need the ability to examine and comprehend every single character.

Principle: Menu and button labels should have the key word(s) first, forming unique labels

Experienced users read only as much of an item name to differentiate among items. Highly experienced users actually trigger on the difference in the external shapes of the entire first word(s) without ever actually reading anything.

Principle: Test all designs on your oldest expected user population

Presbyopia, the condition of hardened, less flexible lenses, coupled with reduced light transmission into the eye, affects most people over age 45. Do not trust your young eyes to make size and contrast decisions. You cannot.

Principle: There’s often an inverse relationship between the “prettiness” of a font and its readability.

Specifically, anti-aliasing softens the edges of a font, giving it a much smoother appearance on the digital page. The problem is that the human vision system responds to sharp edges, so, in smaller font sizes, an anti-aliased font, while often appearing more attractive, can be quite difficult to comprehend.There are anti-alias techniques that specifically increase the sharpness of the edges the eye is seeking, so this is not strictly a black and white issue (so to speak), but it is definitely something of which you should be aware and not something in which every graphic designer has been schooled. You will want to run some reading speed and comprehension tests on proposed font changes.