Thanks so much, Martin, Martyn, Marc and others for your insightful input on 
French Curve. 

>From how the chemist is using the French Curve now, it seems he is using for 
spline. Basically, he has two curves from spectrometry data. To find the 
area underneath one curve without the noise area, he uses French Curve 
MANUALLY (on a piece of paper) and draws the French Curve on one curve (the 
curve of the area interested). Then he moves the French curve parallel to 
the other curve (b). The area underneath where French Curve from the other 
Curve (b) touches on the curve of interested is considered noise area. After 
all these hard work, he MANUALLY uses ruler again and draws the retangular 
bin and tries his best the get the area of interest.

Does it sound like spline work do the job? It would be hard to persuave him 
to use some modern math technique but he did ask me to help him implement 
the French Curve so he can do his work in Excel, rather than PAPER.

Thanks again for your help.

Paul

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