Why set your Barometer to Sea-Level?
Air pressure is measured with a barometer. An 'aneroid' barometer measures the expansion and contraction of an airless metal box as air pressure changes. You can make a simple aneroid barometer to use at home.

Atmospheric pressure is simply the weight of the column of air above your barometer, so this will depend on how high your house or school is above sea-level. Lifting up the barometer by about 8 metres gives a decrease of about 1 mb.

Why is it Important?
You can set your barometer and adjust it to sea-level at the same time by ringing up the nearest weather centre, preferably on a clear and calm day when the pressure will not be changing rapidly or varying much from place to place.

Follow the instructions of your barometer for re-setting it.