based on calculation #3 from this page:http://wahiduddin.net/calc/density_altitude.htmI have the xml for a rough density altitude calculation, if anyone needs one: (A:AMBIENT PRESSURE,millibars) 100 * (>L:pascals,enum) (A:AMBIENT TEMPERATURE,celsius) 273.15 + 287 * (>L:kelvintemp,enum) (L:pascals,enum) (L:kelvintemp,enum) / (>L:calculatedDA,enum) Where: (L:calculatedDA,enum) will give density altitude in kg/m3Steve

Hi,This would be a shorter version (not tested):(A:AMBIENT PRESSURE,Pa) (A:AMBIENT TEMPERATURE,kelvin) 287 * / (>L:CalculatedDA, kilogram per cubic meter)Tom

Hello Skymed,get my ISA and multiply sigma_0 by 1.225http://perso.wanadoo.fr/hsors/FS_Soft/fsdocs.htmlsigma_0 = delta_0 / theta_0Ian