Tristan Wibberley wrote:
....
> Hint though: Logically, you have a hypothesis for what the signal looks
> like (sinusoid) and you want to test that hypothesis for a variety of
> wavelengths until you can spot the most likely match. There happens to
> be a standard technique for doing this very rapidly on a computer and it
> is called an fft.

FFT might be a bit of overkill though. But it's a good idea to check
the spectrum.

I posted some FFT code a while back.
http://groups.google.com/group/comp.lang.c++/msg/49bed9ef02f 1ec9f?