	(SCALAR ADVERB)

	ZLINE is used as a switch or flag.  If ZLINE = TRUE (+1), a
	horizontal line is drawn at Y equal to zero.  If ZLINE = FALSE
	(-1), then the line is not drawn.

	ZLINE is used by : LABEL	PLOT	     SHOW             

	No verbs change ZLINE.

	The initial value of ZLINE is FALSE.

	EXAMPLE :

		ZLINE = TRUE     the next SHOW will draw a zero line at
				 zero intensity.


