Reference for Unix graph/plot utilities

[Heidi Johnson]

Does anyone know of a good reference (book or article) on using
the Unix graph/plot utilities?  Every Unix book I've seen has a
section on nroff, but there is an ominous silence concerning these
plotting tools.  Does anyone have any words of wisdom on this subject
to offer a novice in the graphics world?

All pointers, anecdotes, advice, etc. will be much appreciated.
E-mail to me at    heidi at swift.bcm.tmc.edu.