\fontdimen<f-parameter><f-cs> [= <dimension>]
In TeX, fonts are arranged in tables of 256 characters. In addition to the characters, a number of dimension parameters are given that TeX uses to build a page when using the font. The \fontdimen command allows you to obtain or reset a font parameter value that has already been defined or to define a new font parameter and set its value for a font that has already been loaded. Fonts are loaded with the \font command, which associates a control sequence with the loaded font. The form <f-cs> is such a font control sequence. Each font parameter is associated with an integer <f-parameter>.
Recall that fonts are loaded with the
\font command, which associates a control sequence with a particular font table. The files that make up font tables are placed in a directory or library, and each font table has a given external name which TeX uses to find the table and associate it with a control sequence that can then be used in a source file to change the current font. For example,
associates the control sequence
\roman with the font table that has the external name "cmr10". The font table cmr10 was designed by Donald Knuth, and it stands for Computer Modern Roman at 10 points. This table consists mostly of the Latin alphabet. It has seven parameters. Font tables that contain mathematical symbols have many more parameters. The values
\fontdimen4\roman give respectively the three parts of the inter-word glue for