; NAME:
;	wfcdqc_xy
; PURPOSE:
;       Plots 'y' versus 'x' from a DQC
;	summary db band by band and all bands together
;	if x or y is sky or noise converts to mags/sq.as before plotting 
;	if x or y is date converts to decimal days before plotting
; CALLING SEQUENCE:
;	wfcdqc_xy,db,x,y,[,ps=ps,gif=gif,one_per_page=one_per_page]
; INPUTS:
;	db: summary database
; 	quantity: what to plot. set to either 'seeing', 'am', 'posangle', 
;	'expt', 'ellip', 'sky', 'date' or 'noise'
; OPTIONAL OUTPUT PARAMETERS:
;	ps,gif: indicates output mode. if neither is set, window on screen
;	one_per_page: if set as well as ps, only one plot per page
; RESTRICTIONS:
;	UNTESTED
; CALLED PROCEDURES:
;	
; MODIFICATION HISTORY:
;	18-Feb-2001  Original by S. Aigrain

(See /home/xmmssc/soft/idl/pro/wfcdqc/wfcdqc_xy.pro)