Here is an old post that may help
Gillespie
9th July 2006, 12:37
Leo45 is bang on. I use the exact same method, but to help you remember think of the clock face..
eg, if the wind is 30* off the nose, 30 minutes on the clock is half it's face therefore use half the max drift. 45* = 3/4 of the face so use 0.75ish..so on and so forth...
you can also use the clock face method to mentally calculate ground speed. For wind angles of 0-30* use all the wind, for 30 t0 45 use 3/4, for 45-60 use 1/2, for 60 to 70ish use 1/4 and for any angle beyond ignore it.