Both CAT troff and ditroff need to know the width of each character
that you use.  The widths of each character (along with some additional
characteristics) are arranged in a file for each font.  There are
basically five different width table formats:

	1) CAT troff: uses a binary table of 224 unsigned chars.
	2) MIPS (and RISC/Ultrix) CAT troff uses an ASCII dump of (1)
	3) DWB 2.x and several of the commercial variants use an ASCII
	   format that is compiled into a binary form by a special program
	   called "makedev".
	4) DWB 3.x uses the ASCII format mentioned in (3) - doesn't need
	   to be compiled.
	5) Groff uses the ASCII format mentioned in (4) with minor variations.

If the width tables are wrong, character spacing will look funny - up
to and including overlapping characters, and broken right justification.