NAME:
	oplerr
 PURPOSE:
	Overplot data points with accompanying x or y error bars.
 CATEGORY:
  2-D plotting
 CALLING SEQUENCE:
	OPLERR, [ X ,]  Y , ERR [, DIR= ] [, PSYM= ] [, SYMSIZE= ] [, COLOR= ]
 INPUTS:
	Y = array of Y values.
	ERR = array of error bar values.
 OPTIONAL INPUT PARAMETERS:
	X = optional array of X values.  The procedure checks whether or not
	    the third parameter passed is a vector to decide if X was passed.
	    If not passed, then INDGEN(Y) is assumed.
	DIR = direction to put error bar (default = 6)
	PSYM = plotting symbol (default = +7)
	SYMSIZE = symbol size (default = 1.0)
	COLOR = color for the symbols (default = !P.COLOR)
 COMMON BLOCKS:
	None.
 SIDE EFFECTS:
	None.
 RESTRICTIONS:
	Arrays must not be of type string.  There must be enough points to
	plot.
 PROCEDURE:
	A plot of X versus Y with error bars drawn from the point in the
	direction specified by DIR.  Recognized values for DIR are:

	1	X + ERR
	2	Y + ERR
	3	X - ERR
	4	Y - ERR
	5	X - ERR and X + ERR
	6	Y - ERR and Y + ERR     (default)

	Plot is written to the output device over any plot already there.
 MODIFICATION HISTORY:
	William Thompson	Applied Research Corporation
	July, 1986		8201 Corporate Drive
				Landover, MD  20785

	Marc Buie		Lowell Observatory
	1991 October 11
	Modified to allow specifying the direction for the error bars.
	Change PSYM to a keyword parameter
	1992 June 24, Add SYMSIZE as a keyword parameter
  94/09/14, MWB, added NOCLIP keyword parameter