Kestrel 2500 - Manual (Page 4)

Kestrel® 2500 Pocket Weather® Meter 7
You can obtain your current barometric pressure by checking an internet weather site for
a nearby location, or contacting a local airport. Set this value as your reference pressure on
the ALTITUDE screen to determine your correct altitude: simultaneously press
MAX AVG
and
MAX AVG
buttons to adjust the reference pressure. Press
MAX AVG
or
MAX AVG
to adjust the reference pressure, or
hold
MAX AVG
or
MAX AVG
to adjust the value quickly. You will notice that the altitude will change with
changes in the reference pressure. Simultaneously press
MAX AVG
and
MAX AVG
to exit the reference
pressure adjustment. Set your Kestrel Meter down on a table and allow the altitude reading
to stabilize. (Note: very small changes in pressure generate noticeable changes in altitude.
In order to provide meaningful readings for activities where altitude changes quickly, the
Kestrel Meter features 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: simultaneously press
MAX AVG
and
MAX AVG
buttons to adjust
the reference altitude. Press
MAX AVG
or
MAX AVG
to adjust the reference altitude, or hold
MAX AVG
or
MAX AVG
to adjust the value quickly. You will notice that the barometric pressure will change with
changes in the reference altitude. Simultaneously press
MAX AVG
and
MAX AVG
to exit the reference
altitude adjustment. 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.
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. 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.)