Two fonts at the same size can have vastly different visual sizes. If we recall back to the the Measuring Type lesson, in the days of metal type point size referred to the size of the metal block — not the impression. This carried over to digital type where point size refers to the size of the bounding box — not the letters. When you set a type size, the bounding box is scaled. Some fonts occupy more of the bounding box then others. For this reason you must rely on your eyes to gauge just how big or small a font is.

Please note that type must be evaluated in context. Unless you are selecting a face for screen use, it is imperative that you print each test to accurately evaluate the type.

The x-height is the distance between the baseline and mid-line; it is the same height as the lowercase letter ‘x’. The x-height varies from typeface to typeface. Because 95% of text is lowercase, x-height is a deciding factor in the legibility and readability of a text face and determines the visual size of text. An increased x-height has one of the most noticeable effects on legibility and readability on screen and in print. A taller x-height helps forms appear bigger at text sizes and therefore increases readability.

• In print you typically want to use a font with a medium x-height for body text. This provides a balance between the upper and lowercase letters and brightens the page.

• On screen, you want a taller x-height to give lines more space to distinguish themselves. On screen when pixels are in close proximity they blur together decreasing character distinguishability. A taller x-height forces the counters and apertures in this tight space open, and therefore we get more legible letters on screen.

The x-height comparison test will help you compare x-heights and set an appropriate text size and line-space. These three elements work together to establish the color of a block. When it comes to x-height avoid extremes. As the x-height increases, the length of the ascenders and descenders decreases. Taken to the extreme, this can reduce character legibility. On the other side, if the x-height is too short, ascenders and descender become elongated creating too much white space between lines of text.

One of the single most important legibility features of a text font is character distinguishability, make sure each character is easily distinguishable at your intended font size.

• Line one: Remember the golden rule, differentiation. Look at the !, I, i, l, and numeral 1 to make sure the are distinguishable from each other.

• Line two: Make sure the typeface in question has high contrasting weights and that the bolds are not so bold they fill in.

• Line three: Check that the counters don't close up, particularly look at the problematic letters, a, g, e, and s in regular and bold.

• Lines four & five: Make sure the ascenders and descenders have enough space, particularly look at the f and g.

• Line six: Look at the rounds, b, d, p, q, and o, to see if they are open enough and have the same optical size and color as the square forms, h, n, m, and u.

• Line seven: If numbers are important to your text, look at the 3 and 8, 5 and 6, and 0 and O.

• Line eight: Check the a, a double-storey a is more legible, espically in body text. While your at it, check the italics by contrasting the roman a and italic e.

A fonts spacing can be font-oneed by looking at a particularly problematic groups of letters. The following font-one from Emil Ruder measures the overall quality of spacing by examining color. Problematic words in the left column are contrasted against non-problematic words in the right column. What you want is an even color between the two columns. If need be, adjust the tracking or letter-spacing.

A fonts spacing can be font-oneed by looking at a particularly problematic groups of letters. The following font-one from Emil Ruder measures the overall quality of spacing by examining color. Problematic words in the left column are contrasted against non-problematic words in the right column. What you want is an even color between the two columns. If need be, adjust the tracking or letter-spacing.