I use the 10 deg fan line method and it works fine. Remember that it is only giving ball park figures on a whizz wheel as you are working with forcast winds and the actual wind may be incorrect. I would use as simpler method as you can, that way maximising the time you spend looking out the window. I don`t like the idea of a whizz wheel used during flight. Even if you are very good you are taking your eyes into the cockpit and away from that lookout.
