"Sriram Narayan" wrote in message news:1105397045.6c0b9af7d0985bd99dd3e30aa7ae44ee@t eranews...



That still wouldn't help since the pressure change for a 1000ft change in
altitude at 18k would be smaller than at sea level. It would have to have
some non-linear spring compensation as a function of absolute pressure.



The USA is just now getting into the RVSM rules which allow vertical separation of 1000 feet. Used to be 2000' minimum
for all of these reasons....