Type size is expressed in units called ”points.“ A point is very close to 1/72 inch, so close that it's often defined as exactly 1/72 inch. The point size indicates the height of the characters. For instance, when we speak of 12-point type, we're referring to characters that are 12/72 (1/6) inch high from the top of the ascenders to the bottom of the descenders.
In Windows, another convenient measurement is the ”twip“; this fabricated word stands for ”twentieth of a point,“ which equals 1/1440 inch. Note that the pixels-per-logical-inch measurements associated with each of the five sets of GDI raster fonts are such that the size of each pixel is an integral number of twips. Or rather, each pixel is an integral number of a measurement we can call ”logical twips“:
| Pixels per Logical Inch | Logical Twips per Pixel |
| 48 | 30 |
| 60 | 24 |
| 72 | 20 |
| 96 | 15 |
| 120 | 12 |
If you run the EXEHDR utility on the COURx.FON, HELVx.FON, TMSRx.FON, and SYMBOL.FON font resource files, you'll see in the module description that the files contain fonts of particular point sizes. The COURx.FON files comprise 8-point, 10-point, and 12-point fonts. The HELVx.FON and TMSRx.FON files include those sizes and add 14-point, 18-point, and 24-point fonts. But here's the catch: These point sizes are dependent on the resolution given by the number of pixels per logical inch. For instance, the 24-point Times Roman font in the TMSRB.FON file has characters that are 24 pixels high. Only on a display that has 72 pixels per vertical inch will the 24 pixels correspond to a 24-point font.