8. Go to the calibration settings page and observe the “REL Barometer
value (this is the value we just adjusted in step 4 above). Compare the
REL value with the value from the airport. IN our example, the REL
display was 1022.9 where we expected 1019.1. This then tells us that our
displayed REL pressure is 1022.9 – 1019.1 = 3.8 hPa different from the
reference source.
9. Since we assumed the absolute pressure measured was correct, and we
presumably calculated the elevation related offset correctly, we must
conclude that the absolute pressure was not correct after all. It appears to
be 3.8 too high, so we’ll now enter a correction of -3.8 in the settings for
“ABS Barometer” until it reads a value 3.8 hPa lower than before. This
kind of correction is entirely normal as during manufacturing small shifts
in the pressure sensor readings can be introduced.
10. For a more precise procedure, locate a very precise barometer that you
can place right next to the console, you would adjust “ABS Barometer”
until the ABS pressure reads identical. You would then still adjust “REL
barometer” until it displays the value from the reference airport. This
procedure would also produce the correct relative pressure, but due to a
precise calibration of the absolute pressure, it too is correct.
The first procedure above generally works quite well, but for stations at fairly
high altitudes (e.g. 5,000 ft. or higher) it may be more incorrect than at lower
altitudes. In such cases comparisons with other known correct, and nearby at
similar altitude, stations may help.
Now that calibration is complete, feel free to change the pressure units to
whatever you like.
Note: Airport METAR data is often only updated every 10, 15 or even 30
minutes. If you use the information in the procedure above, you may
be looking at pressure data that is out of date by as much as the update
interval. To get best results observe several times and figure out the
update interval and then use two values for the procedure: one taken
immediately after an update, another taken about halfway through the
interval.
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