Stefan wrote:

And when exactly are you going to calculate all this? :-P

On downwind leg, and I won't do the full calculation. Something like 90
degrees= nil wind, 60 = half wind, 30=full headwind. In the example this
gives me +0, +5 or +10. Close enough.

If your glider floats well, like my Open Cirrus, then the extra few
knots is significant. If I land 10kt over the correct speed for the day,
I'll float more than twice as far after the roundout.