Since we don't (yet) have AOA gauges...
Kirk
66

If you want to buy one they are available. Check out www.safeflight.com
There are more listed on page 16 and 17 of the Feb 2008 issue of
Soaring.

Trying to thermal effectively while keeping your speed within a 2-3
knot range sounds
like trying to balance on a ball. I suspect the slight difference in
efficiency is not significant.