Ambient Weather Support

To calibrate relative pressure to sea-level on the display console:

1. Press and hold the BARO button for 2 seconds to enter barometric mode. The icon RELATIVE or ABSOLUTE will flash.Make sure the RELATIVE Pressure is showing on the display. If ABSOLUTE Pressure is showing, switch to RELATIVE pressure per Section 5.10.2.
2. Press (do not hold) the BARO button again. The relative pressure will flash.
3. Press the [ ] button to increase the relative pressure and the [ ] 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).

Relative Pressure Discussion:

The console 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.