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5.4
Barometric Pressure Display and Settings
5.4.1
Barometric Pressure Units of Measure
In normal time mode, press the
BARO
button to change barometric units of measure (hPa / inHg /
mmHg).
5.4.2
Absolute Pressure vs. Relative Pressure
Press and hold the
BARO
button for 2 seconds to enter barometric mode, and press the
+/CHANNEL
button to switch between the relative and absolute pressure reading.
5.4.3
Relative Pressure Calibration
Please Reference Section 5.4.3.1 for details on the purpose of calibrating relative pressure, and how
to calibrate relative pressure in your area.
1.
Press and hold the
BARO
button for 2 seconds to enter barometric mode. The icon
BARO
will flash.
Make sure the REL Pressure is showing on the display. If ABS Pressure is showing, switch to
REL pressure per Section 5.4.2.
2.
Press (do not hold) the
BARO
button again. The relative pressure will flash.
3.
Press the
+/CHANNEL
to increase the relative pressure and
-/MEM
to decrease the relative
pressure.
4.
Press (do not hold) the
BARO
button again to exit the relative pressure calibration mode, or
wait 60 seconds to time out.
Note: After calibration, the barograph will reset to 0 change (flat line across the graph).
5.4.3.1
Relative vs. Absolute Pressure and Calibration
The clock displays two different pressures: absolute (measured) and relative (corrected to sea-level).
To compare pressure conditions from one location to another, meteorologists correct pressure to
sea-level conditions. Because the air pressure decreases as you rise in altitude, the sea-level corrected
relative pressure (the pressure your location would be at if located at sea-level) is generally higher
than your measured absolute pressure.
Thus, your absolute pressure may read 28.62 inHg (969 mb) at an altitude of 1000 feet (305 m), but
the relative pressure is 30.00 inHg (1016 mb).
The standard sea-level pressure is 29.92 in Hg (1013 mb). This is the average sea-level pressure
around the world. Relative pressure measurements greater than 29.92 inHg (1013 mb) are
considered high pressure and relative pressure measurements less than 29.92 inHg are considered low
pressure.
To determine the relative pressure for your location, locate an official reporting station near you (the
internet is the best source for real time barometer conditions, such as Weather.com or
Wunderground.com), and set your weather station to match the official reporting station.
