Yes you're right, it's just one I quickly found online and the TAS scale is wrong now I look at it. I was just looking at the lay of the lines for the OP's original question. Getting "knowledge" from the internet is a dangerous pastime haha. The simpler version I was thinking of just has 3 lines, with any one speed constant the other 2 will diverge with increasing altitude and converge with decreasing altitude, thats all.