Hey, those other threads are interesting. I'll enclose an old GPS plot just for fun -- I did it on a windsurfer back in 2000, the plots with a Matlab script, overlaid on aerial photos. Hopefully someone will find it amusing. Orange is about 25 kts, BTW. The associated polar plot is scattered all over the place, of course, because the wind direction changed so much from one end of the trip to the other.

Anyway, all this discussion has gotten some ideas going; I'll try to do some research and experiments with wind calibration this (Northern) Summer. Thanks for the links and tips.