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+	    ECHELLE DISPERSION FUNCTION FITTING KEYS
+
+
+CURSOR KEY SUMMARY
+
+?  Help             c  Print coordinates             d  Delete point
+f  Fit dispersion   o  Fit with fixed order offset   q  Quit
+r  Redraw graph     u  Undelete point                w  Window graph
+x  Set ordinate     y  Set abscissa                  I  Interrupt
+
+
+COLON COMMAND SUMMARY
+
+:show               :function [value]   :highreject [value]   :lowreject [value]
+:niterate [value]   :xorder [value]     :yorder [value]
+
+
+CURSOR KEYS
+
+?  Print this list of cursor keys
+c  Print cursor coordinates
+d  Delete the nearest undeleted point to the cursor
+f  Fit dispersion function including determining the order offset
+o  Fit dispersion function with the order offset fixed
+q  Quit and return to the spectrum display
+r  Redraw the graph
+u  Undelete the nearest deleted point to the cursor (may be outside the window)
+w  Window the graph (type ? to the window prompt for more help)
+x  Set the quantity plotted along the ordinate (x axis)
+y  Set the quantity plotted along the abscissa (y axis)
+I  Interrupt the task immediately
+
+
+COLON COMMANDS
+
+:show		     Print current function and orders
+:function [value]    Print or set the function type (chebyshev|legendre)
+:highreject [value]  Print or set high rejection limit
+:lowreject [value]   Print or set high rejection limit
+:niterate [value]    Print or set number of rejection iterations
+:xorder	[value]	     Print or set the order for the dispersion dependence
+:yorder [value]      Print or set the order for the echelle order dependence
+
+
+The dispersion function fitted is given by a two dimensional function
+(either chebyshev or legendre) of the pixel position along the
+dispersion of an order (called x) and the order number (called y).  The
+order number is determined from the aperture number by an offset and
+direction of increasing order number.  The basic order dependence is
+separated from the surface function as given below.
+
+	y = offset +/- aperture
+	wavelength = f (x, y) / y