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There are different manners in which to handle this adjustment. We will
outline a reliable procedure below, which requires adjusting both pressures.
The method assumes that you have an official airport sufficiently nearby to
act as a reliable reference. Usually distances of up to 25 miles work reliably,
but this is not always true and depends on geography. We start by assuming
that your station’s absolute pressure reading is correct and needs no offset
correction.
The procedure below assumes you are starting from the gateway’s factory
setting. With those settings, ABS and REL should, at this time, be
displaying the same value. We also assume, for the moment, that ABS
pressure is 100% correct.
1.
For this procedure we will get the most precise results if our display for
pressure is in hPa units. Even if you do not want to use those units
eventually, set the app to use them for now.
2.
Determine the altitude, or elevation above sea level, of your station’s
gateway. This measurement is necessary to account for the difference in
air pressure caused by the elevation of your gateway. Elevation above
sea level reduces the absolute pressure measured by your sensor.
Determine this altitude using a GPS, or look it up using a tool such as
https://www.freemaptools.com/elevation-finder.htm
. You
can input your location’s GPS coordinates, or manipulate the map to
your location. Click on “Estimate Elevation” and observe the result. For
an example we will use a gateway location at 42 ft. above sea level.
3.
This tool will provide the ground level elevation at your location, so
you will need to add the right amount for how high above ground level
your gateway is. If you are on a ground floor and have the gateway on a
desk, you’ll have to add something like 3-4 ft. If you are using a GPS
system that tells you elevation, make sure it is right next to the gateway
and you’ll be able to read the correct elevation right from the GPS
results without further adjustment.
4.
With the correct altitude/elevation in hand you will need to determine
the correct offset. To be added to the absolute pressure reading in order
Summary of Contents for GW1003
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