By default, plt makes an X11 screen
plot. To make a printed plot, use the option -T lw, and pipe the output
of plt to lwcat. Under Unix or Linux, lwcat uses the standard lpr
print spooler to send plt's output in PostScript format to the default
printer. Under MS-Windows, or using lwcat's -gv option under Unix or Linux,
the PostScript output is displayed on-screen using GhostScript (GSView under MS-Windows, or gv otherwise; these programs can save the output
in a file or send it to a printer).