Sans serif fonts like Arial do not feature these little strokes, as you can see Figure 1. On computer screens, sans serif fonts are preferable, because relatively low screen resolutions—typically around 100 pixels per inch rather than the 800 dots per inch of print—make serif fonts look fuzzier, especially in small sizes.
The new generation of e-books such as the Kindle from Amazon have much higher pixel densities than current PC monitors—around 170 ppi. This makes it possible to use serif fonts—as in a real paper book—improving the overall user experience. So the choice between serif and sans serif fonts depends on the capabilities of the target output technology.
In the mechanical printing process of the past, printers manually assembled individual letters into words and sentences. Miniscule letters—a, b, c, and so forth—were stored in cases that were placed below those that held majuscule letters—A, B, C, and so on. Hence, we now call them lowercase and uppercase letters.
There are three major ways of using letter cases in text, as shown in Figure 2: lowercase, mixed case, and uppercase. We see all three in our daily lives. Ergonomists have consistently recommended using mixed case letters and shy away from using all uppercase letters, especially for continuous text.
Their reason for recommending mixed case is that the ascenders—extensions toward the top, as in b, d, f, h, k, l, and t—and descenders—extensions toward the bottom, as in g, j, p, q, and y—create the typical shape for a specific word . It is, therefore, easier to recognize words in mixed case while reading. Mixed case also allows better comprehension of the sentence structure, since uppercase applies only to the first letter of the first word at the beginning of a sentence or to proper names.
Interestingly, recent research yields opposing findings. Experiments show that, because of its sheer size, all uppercase is more legible, in terms of reading speed, than the other letter cases, especially for visually impaired persons. 
Now try reading the previous paragraph in all uppercase.
INTERESTINGLY, RECENT RESEARCH YIELDS OPPOSING FINDINGS. EXPERIMENTS SHOW THAT DUE TO THE SHEER SIZE, UPPERCASE IS MORE LEGIBLE IN TERMS OF READING SPEED THAN THE OTHER LETTER CASES, ESPECIALLY FOR VISUAL IMPAIRED PERSONS.
You can judge for yourself what letter case style is easier and faster to read. I personally believe that mixed case is superior, at least for users without vision impairments.
When displaying continuous text on informational Web sites or in online Help, there are two common ways of aligning the text, as shown in Figure 3:
- justified—The text body has clean edges at both the left and right.
- ragged right—The text body is left aligned.
Although justifying continuous text provides a nice block of text, the extra spaces that appear between individual words often create continuous vertical spaces that can appear meaningful—like vertical rivers of white. This can be distracting to readers . It is, therefore, recommended to use ragged-right text alignment.
Different layouts may require different text orientations. Figure 4 shows standard horizontal text; marquee style text, in which each individual letter is horizontal, yet the letters are vertically aligned; and text that is rotated by 90° to the right or left.
Obviously, in the western world, it is best to use horizontal text. After all, our books are not printed in marquee or rotated text. Though this may not be the case for other cultures.
Research confirms that people can read text with a horizontal orientation the fastest . It has also shown, from a usability standpoint, that it does not matter whether text is rotated to the right or the left—for example, on vertical tabs. Reading speed is a function of where the items appear on the screen. However, for aesthetic reasons, the font should be directed inward. Of all text orientations, marquee is the hardest to read and yields the poorest reading performance.