Thanks for that Jim.
Obviously you are much better at web search than I.
Pity they haven't got the HiTran & LoTran atmosphere model data in native single file form. With a following wind I think I can remember how to deal with that. But then I might be tempted to do a full job instead of sorting simple figures as a green pundit stopper.
Mayhap I'll report back in a couple of months if it all turns out how I expect.
I can't face it as a full time job but it will make a nice break from restoring a Pratt & Whitney Model B lathe.