CURVE

     CURVE is a number corresponding to the method to be used to fit the 
     curve.  Generally, CURVE should be set to 2.
 
     The curve types currently available are:
 
	1	-	piecewise straight line
	2	-	cubic spline 
	21	-	cubic spline with linear ends
	22	-	cubic spline with parabolic ends
	23	-	cubic spline with extrapolated ends

     Note that types 2 and 21 are the same.  Types 22 and 23 produce
     slightly different results at the ends of the splines.