At start the instrument adjustment menu always shows the pressure to be 29.92 HG and Generally, the needle is at 900 though sometimes it will slowly drop to a slightly lowerįigure (I don't know what in the program causes this). Nevertheless that's not how it's programmed. Yes, you can adjust the altimeter to the field elevation ( around 20 feet) using the instrument setting menu, but when you do so, the pressure drops to around 29.0 or so inches, which is incorrect, since the instrument should be calibrated to read 0 feet at 29.92 pressure, not 900. It consistently comes up showing 29.92 at start, even though the altitude is 900 feet or so. But if it reads higher, the instrument setting menu should reflect a commensurate lower pressure, which it does not. It's understandable that the gauge will read higher at a lower atmospheric pressure-that's what it does. This time, quite inexplicably, it read 780 ft as at KSFO with the instrument setting menu showing 29.92 HG, which should not be. I just went back and rechecked the A6 at San Diego. I don't know how this has been programmed in flight gear. When properly calibrated, the gauge will always read 0 altitude when the atmospheric pressure is 29.92 inches HG. It is adjusted according to standard atmosphere. To calibrate the instrument an instrument maintenance person has to adjust the physical linkage between the needle and the bourdon tube. When the outside pressure drops the tube straightens causing the needle to turn to a higher setting. The issue is how the instrument is calibrated. I understand what you are saying, but that is not the issue.
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