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of 0 are appropriate and correct, this generally cannot be done for
relative barometric pressure readings. To understand consider the
following.
Absolute barometric pressure can be calibrated at manufacturing time
by comparing with a precise instrument that measures pressure at the
same location. In practice, sometimes small adjustments of a few hPa
may be needed. The relative pressure represents what the air pressure
would indicate if your station was at sea level and depends on the
altitude of your console and cannot be known in advance. This is why it
needs an offset adjustment.
There are different manners in which to handle this adjustment. We will
outline a reliable procedure below, which requires adjusting both
pressure offsets. 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 assum
ing that your station’s absolute pressure
reading is correct and needs no offset correction.
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 console to use them for now.
2. Determine the altitude, or elevation above sea level, of your station’s
console. This measurement is necessary to account for the difference in
air pressure caused by the elevation of your console. 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
this web site:
https://www.freemaptools.com/elevation-finder.htm
. You
can input your location’s GPS coordinates, or manipula
te the map to
