The barometer must be hung on a wall or a post. It will not work properly lying flat on a table, for
instance. Let it hang for a minute before taking a reading. There are four scales on the dial.
- The inner scale describes the weather in words, such as stormy. This is only a guide and is rarely useful.
- The next scale is millibars, or hectopascals (hPa), the unit used by the Bureau of Meteorology in Australia.
- The third scale is millimetres of mercury, which simulates the reading from a liquid mercury barometer
(details over the page).
- The fourth scale is inches of mercury. Imperial units that are not used in Australia any more.
If you know how high your town or suburb is above sea level, you can convert your air pressure reading to the mean sea level
(MSL) pressure. Divide your altitude (in metres) by nine, then add that number to your barometer reading in hectopascals.
Now you can compare the result with readings on the Bureau's MSL analysis and forecast charts.
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