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How do I get a setting for my barometer?
Atmospheric pressure varies over time and space and also varies
with height. Since the altitude of the barometer normally stays
constant (the station height) a correction is made to the reading
to make it equivalent to the mean sea-level reading. This is done
so that readings from different locations can be compared, with
differences due to height being removed. Aneroid barometers are
normally adjusted to mean sea-level values - read the barometer's
instructions to see how to adjust the instrument (normally by
a screw on the back). Mercury barometers cannot be adjusted (don't
tamper with them because a mercury spillage is a health hazard).
To get the value for your barometer, choose a high-pressure day,
pressure values are not changing very much - you can watch the
TV forecasts for such a day. Go to the Met
Office's observation page and choose the station nearest to
your location - on a quiet weather day the distance away from
you will not be significant. Adjust the barometer to the station's
pressure value. You can check your barometer on other days but
will have to compensate for fast-changing pressures or distance
if the pressure is low or changing fast. The observation includes
information about how the pressure is changing. There is a page
on the University
of Reading web site which gives more information about barometers.
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