Kestrel
®
4000 Pocket Weather
®
Tracker
barometric pressure. Your altitude as shown on the ALTITUDE screen will change as the weather changes,
but you can ignore this screen for this purpose.
If you are planning a day hike would like to track your altitude, you’ll need to enter the correct reference
pressure on the ALTITUDE screen as described above in “starting with the known barometric pressure.”
You can now track the altitude changes as you hike. In this instance, you should ignore the values on the
BARO screen, since the pressure changes will be due to changes in elevation far more than to changes in
the weather.
In general, changes in barometric pressure associated with weather changes are small over the course of
one day, but they will affect the accuracy of the altimeter over time. This is why aircraft reset their altimeters
at every airfield by entering the field’s “altimeter setting” or reference pressure. Accordingly, if accurate
altitude readings are your primary interest, you should reset the reference pressure on your Kestrel Meter
regularly. If you encounter an elevation landmark, you can adjust the reference pressure until the altitude
matches the landmark elevation. This will correct the altitude for any pressure changes due to the weather.
(Or, you can obtain an updated reference pressure from the sources described above.)
Some final notes - If you wish to know the actual or station pressure for your location (such as for engine
tuning), simply set the reference altitude on the BARO screen to “0”. In this case, the Kestrel Meter will
not make any adjustment and will display the measured value. (Engine tuning and ballistics software
sometimes refer to atmospheric or station pressure as “absolute pressure.” These applications are
concerned with the actual air density, as opposed to pressure gradients relating to weather, so barometric
pressure is less useful.)
Also, the above discussion applies to ALL pressure altimeters, including one you may have in a watch or
other device, but not to GPS altimeters, which use satellite triangulation to determine altitude. Note that
with present GPS technology, pressure altimeters remain more accurate for measuring altitude change. This
is why airplanes still rely on pressure altimeters, not GPS.