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on 5.2.
9.3
Temperature Changes
The temperature sensor is a resistive thermal device (RTD). As the temperature changes, the resistance
of the device changes and this resistance translates to temperature.
The RTD is inside the unit and subject to a thermal time constant (or the time it takes for the entire
display to reach a given temperature due to the mass of the display). Thus, rapid changes in
temperature may take several minutes to stabilize. If the display is close to your body, it will not
accurately measure the ambient temperature, and may take several minutes to stabilize when away
from your body warmth.
Thus, it is best to hang the display from the carbineer in the open air to accurately measure the
ambient temperature.
9.4
Pressure Altitude vs. True Altitude
Altimeters are often misunderstood because they do not measure your actual position on the earth
(true altitude) such as a GPS, but measure the air pressure and predict the altitude based on this
measurement. This is referred to as “Pressure Altitude”.
Pressure Altitude is adversely affected by the true altitude and to a lesser extent, changes in the
weather, often referred to as barometric pressure changes.
Thus, your Pressure Altitude can change without changing your position. These changes can be as
great as a thousand feet (the changes due to weather are more pronounced at higher altitude).
To offset the difference between Pressure Altitude and True Altitude, you must calibrate the device at a
known altitude, whenever convenient. For more information on altitude calibration refer to
Secti
9.5
Relative Pressure vs. Sea-level Pressure
Relative Pressure is the pressure measured at your location, and Sea-level Pressure is the pressure
compensated to sea-level.
To compare pressure conditions from one location to another, Meteorologists correct pressure to
sea-level conditions, removing the altitude affects.
Because the air pressure decreases as you rise in altitude, the sea-level corrected pressure (the pressure
your location would be at if located at sea-level) is generally higher than your measured pressure.
Thus, your pressure may read 28.62 inHg (969 hPa) at an altitude of 1000 feet (305 m), but the
corrected pressure is 30.00 inHg (1016 hPa). The standard sea-level pressure (the average sea-level
pressure around the world) is 29.92 inHg (1013 hPa).
Pressure conditions greater than 29.92 inHg (1013 hPa) are considered high pressure and pressure
conditions less than 29.92 inHg (1013 hPa) are considered low pressure.
This device calculates the sea-level barometric pressure based on the calibrated altitude described in
the previous section.
9.6
Digital Compass Measurement
The compass must be level to accurately measure bearing. This can be done by placing on a flat
surface (best), or in the palm of your hand. This is common with most digital compasses (some
