galaxy flyer,
Sorry, I got a bit ahead of myself there. Yes, if you imagine the line from 330 degrees on the RMI outer edge to the centre of the RMI as being equal to 30 knots in strength then, after using your calculations, place the headwind and crosswind visually on the RMI it does indeed show you the wind is from 330 degrees. But this is from a starting position of knowing the wind is 30 knots in strength, and when I'm up there I wouldn't know this. If I were to imagine this line as being equal to 40 or 50 knots, putting in your calculated headwind and crosswind would give an inaccurate direction for the wind. So excuse me if I'm being completely stupid here but how do I prove that the radius of the RMI equates to the strength of the wind? Or rather, how do I prove this is equal to the value of 30 knots?