Kestrel 4500 - Manual (Page 9)

Kestrel ® 4500 Pocket Weather ® Tracker 17
rapid altitude response. This is why the altitude readings tend to fluctuate by a few feet.) After obtaining
a current altitude from the ALTITUDE screen, move to the BARO screen and enter this value as your
reference altitude by following the same procedure. Both readings will now be accurate.
Starting with a known altitude for your location
You can obtain your altitude from a topographical map or local landmark. Google
Earth is an excellent free program that provides the exact altitude for any given
address: www.earth.google.com/. Set this value as your reference altitude on the
BARO screen to determine your barometric pressure: Press the button to enter
the reference setting mode. Press the button to increase the reference altitude or the button to
decrease the reference altitude. You will notice that the barometric pressure will change with changes in
the reference altitude. Press the button to exit the adjustment mode. Again, allow the Kestrel Meter to
stabilize, then enter the value from the BARO screen as your reference pressure on the ALTITUDE screen
by following the same procedure. Both readings are now accurate.
When reviewing stored data, remember that changes in pressure AND changes in location/altitude will
affect the stored values. When tracking pressure changes relative to weather, set the reference altitude
on the BARO screen and keep the Kestrel Meter in one location. Your graph history will now show trends
in 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.
Finally, the DENSITY ALTITUDE screen is calculated from the absolute values of station pressure, relative
humidity and temperature, and is not affected by the reference values entered in the BARO and
ALTITUDE screens.