Irlandes, further to my last post I have been very boring and used your three examples of constant DA and checked using the gas constant, temperatures in Kelvin and accurate pressures from ISA and the Density in all 3 is within 0.0001 kg/m3. So there is no mysterious change in DA caused by altitude vs temp and I can only conclude again that the Robinson graphs are crap. DA is DA is DA so the answer to why you get 3 different AUM for 3 identical DAs can only be answered by Uncle Frank.