29
Codes
” at
https://www.world-airport-codes.com
or a similar reference.
Enter your location or nearby airport name, and press “Search.” Select
the correct airport from your search results and click on it. For example,
search for “Mountain View” and click on “Moffet Field.”
6. From the resulting page find the ICAO code, if listed. Otherwise use
the IATA code. For the example above, you would find IATA code
“NUQ.”
7. Now go to a web site like
AVIATION WEATHER CENTER
(for US
locations) at
https://www.aviationweather.gov/metar?gis=off
and enter
the code you found in step 2, and click “Decoded” (to make the next
step easier) before requesting the METAR information. For the example
we would enter “KNUQ” and find a result output like: “30.09
inches Hg
(1019.0 mb) [Sea level pressure: 1019.1 mb
]”
8. Make sure your console is displaying REL barometric pressure and
compare its 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 an offset of
-3.8 in the
settings for ABS PRESS OFFSET.
10. For a more precise procedure, locate a very precise barometer that
you
can place right next to the console, you would adjust “ABS PRESS
OFFSET” un
til the ABS pressure reads identical. You would then still
apply the calculated “REL PRESS OFFSET” as above, and then, as a
final step, further adjust “REL PRESS OFFSET” until it displays the
reference value from the airport. This procedure would also produce the
correct relative pressure, but due to a precise calibration of the absolute
