I've edited the graph in post #11 to show more clearly what it represents.
I removed the AoA curve because it is not relevant to the question being addressed, and also because the AoA's seem to be less well defined than the L/D values.
The two curves in red show the variation of L/D vs Mach at a particular weight at two altitudes, FL150 for the left curve and FL350 for that on the right. Many of those curves could be drawn to cover all altitudes and weights. The blue line connects the maxima of all the 'red' curves that could be drawn. So any of those curves, for whatever weight and altitude, will have a maximum L/D that lies on the blue line.
Last edited by HazelNuts39; 19th August 2013 at 16:16.