The Ahem font was developed by Todd Fahrner to help test writers develop predictable tests. The font's em square is exactly square. Its ascent and descent is exactly the size of the em square. This means that the font's extent is exactly the same as its line-height, meaning that it can be exactly aligned with padding, borders, margins, and so forth.
The font's alphabetic baseline is 0.2em above its bottom, and 0.8em below its top. The font has an x-height of 0.8em.
The font has four glyphs:
- 'X' U+0058 A square exactly 1em in height and width.
- 'p' U+0070 A rectangle exactly 0.2em high, 1em wide, and aligned so that its top is flush with the baseline.
- 'É' U+00C9 A rectangle exactly 0.8em high, 1em wide, and aligned so that its bottom is flush with the baseline.
- ' ' U+0020 A transparent space exactly 1em high and wide.
Most other US-ASCII characters in the font have the same glyph as X.