NAME:
	plotsn
PURPOSE:
	Analyze a vector and retrieve the signal-to-noise ratio.
DESCRIPTION:
	First, fit a polynomial to the data, subtract the polynomial and
	add the mean of the polynomial to flatten the data.
	Compute the mean and standard deviation in the flattened data.
CATEGORY
       Spectroscopy
CALLING SEQUENCE:
	plotsn,point1,point2,x,y,label
INPUTS:
	point1   = First data point to use from x and y.
	point2   = Last data point to use from x and y.
	x        = 1-d vector containing independent variable.
	y        = 1-d vector containing dependent variable.
	label    = String title for plot.
OUTPUTS:
	None
REVISION HISTORY:
	Written by Marc Buie on 2/27/91
COMMENTS:
	A single number for the SNR is somewhat dubious if the data spans
	a wide numeric value.