Dear Allan,

Sorry - the reason I missed you out of the summary is that your original
mail didn't have the [BIOMCH-L] tag on it and so got seperated from the

I do think your method is unnecessarily complicated though. Am I missing
something? e.g. why do you need to define a unit vector?

Incidentally, I now realise that the simplest possible method is:

angle = ATAN2(x,y)
If angle < 0 THEN angle = angle + 2 pi

This was submitted by Zong-Ming Li, although several people suggested
it. I have checked it, and included it in the spreadsheet:

Dr. Chris Kirtley MD PhD
Associate Professor
Dept. of Biomedical Engineering
Catholic University of America
620 Michigan Ave NE, Washington, DC 20064
Tel. 202-319-6247, fax 202-319-4287

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