Dash
The dash d command instructs plotl to use a dashed
line (the dash length being defined by d) with equal
mark and space for data curves.
NoDash
The command nodash returns the data curve to the default,
solid, line.
Mark/Space
The command pair, mark dm and space ds determine
the mark and space of a dash. For example, issuing the commands
mark 0.1
space 0.5
would cause data curves to be dashed with pend down for 0.1 inch, and
pen up for 0.5 inch.