I hate to bring this back up again after so much work has been done to improve

it, but I still see an important issue with it. There appears to be something

wrong with the relationship between QNH and the ambient pressure at that

location. As an example, I located the airplane at a high elevation airport

(SLLP) in La Paz, Bolivia. Using real weather the METAR indicated a QNH of

1037. The altitude simulation variables are shown in the following screenshot:

ambient pressure at the airport of 635.45 hPa for the QNH of 1037 and airport

elevation of 13,313 ft. However, for that elevation and QNH, the ambient

pressure should be 627.57 hPa. The MSFS pressure leads to a pressure altitude

of 12,355 ft, but it should really be 12,670 ft. A QNH of 1037 should shift

the pressure vs altitude curve down by 642.5 ft. If the ambient pressure is

really 635.45 hPa at the field elevation of 13,313 ft, then the QNH should be

1048.8. My calculations are based on the following equations from the Boeing

Jet Transport Performance Methods document (with 1013.25 hPa substituted for

29.92 in Hg as the sea level pressure).

This is a stumbling block for us

in trying to implement the effect of barometric pressure compensation since

what we would be basing it on (the equations above) are different than what

MSFS appears to be using.