The thinnest line a LaserWriter can print is limited by what's known as a
device pixel. With all LaserWriter models to date, including the Personal
LaserWriter (using the Canon P-110 engine), a device pixel is 1/300 of an
inch, or .08mm. This translates to 24/100, or roughly one quarter of a
point.
Many programs won't actually display a line this narrow, and instead use
one point as their smallest printable unit. This PostScript code will
generate an example page with a matrix of lines, each a single device pixel
thick:
0 setlinewidth
72 72 612 {dup 0 moveto 792 lineto stroke} for
72 72 792 {dup 0 exch moveto 612 exch lineto stroke} for
showpage
Use a PostScript dump utility to download this program. This feature
is available in version 7 of the LaserWriter Font Utility, or one of the
old standbys like PSDump or Widgets.