Oregon Scientific WS6762 Mode D'emploi page 45

Reading the barometric pressure for the last 12 hours
Press the HISTORY ABS /REL button (38) repeatedly to read the barometric pressure values for the last 12 hours.
0HR = present barometric pressure
–1HR = barometric pressure an hour earlier
–2HR = barometric pressure two hours earlier, etc.
...............
–12HR = barometric pressure twelve hours earlier, etc.
Adjusting the air pressure indication
The forecast of this weather station is basing on an analysis of the change of the air pressure.
The barometric pressure (30) is factory provided adjusted to the absolute air pressure. As the air pressure generally decreases with the height beyond sea level,
the public weather service always announces the so-called relative air pressure. This relative air pressure is adjusted to the topography of the country in order to
get comparable values.
You can adjust the air-pressure of your weather station to the proportion of its place. For that you have to adjust your weather station uniquely the current air
pressure. Ask your local weather forecast service for the barometric pressure at sea level or get the current value from the Internet.
You can adjust the weather station like this:

Press and hold the HISTORY ABS / REL button (38) for approx. 3 seconds. After that press the + or – button (35), (36), to interchange between the
absolute or relative air pressure.

Chose „Rel" and press the HISTORY ABS/REL button for confirmation. The air pressure indication blinks. Now you can chose the correct value by
pressing the + or – button.