Each PLOT statement produces a separate plot. The plotting symbol is
the first character of the formatted value of the symbol variable:
K for Kreitz;
L for LaGrange. POS= specifies that each plot uses 25 print positions
for the horizontal axis. OVPCHAR= designates the exclamation point as the
plotting symbol when the plotting symbols coincide. NOSYMNAME suppresses the
name of the symbol variable Seller from the second listing.
plot stove=seller / pos=25 ovpchar='!';
plot icebox=seller / pos=25 ovpchar='!' nosymname;