pgplot plotting routines need user to place a directory in path

In your .cshrc, you must add /usr/share/astro to your path if you want to be able to see
plots on screen with /xwin or /xserv windows, because pgplot has to be able to find the pgxwin server in that directory at execution time. Joel linked the pgxwin server from its home in /uasr/share/astro/pgplot into /usr/share/astro to make it more findable.
eg; in Joel’s .cshrc, one finds
set path = ( . $path /usr/share/astro /usr/share/astro/idlshare/gbtidl/)