The only data I have is current air pressure and temperature. Everything else must be estimated/predetermined. Commercial altimeters are able to sense the ambient air pressure and calibrate that to mean “0 ft”. From there, sensing the difference in pressure as you climb, they can derive the altitude. I don’t mind a little bit of error, it’s just that I can’t find a formula that will do that. Every formula I try gives the wrong answer. Thank you very much for your help.