DCL:GRPH1:SCPACK: User Interface
This is a group of subroutines for polymarker primitives.
When the internal variable 'LMISS' handled by glpget/glpset
is set to .true., then missing-value handling is performed.
In other words, markers will not be placed on missing values.
Also, by changing the internal variable NPMSKIP' (See Section 2.4.4),
settings can be made to display every nth marker.