All air has weight. It may not be readily apparent to us because it’s mass is so small, but it does have mass and that means it has weight. In fact, all the air that sorrounds the earth weighs 5600 trillion tons, can you believe that? The weight of air over a given area is called air pressure or even barometric pressure.
Air pressure is measured by the barometer. The barometer measures air pressure in a given location. Of course air pressure differs across the earth surface and even at different altitudes. For example, colder air is heavier than warmer air so cold air has higher pressure than warm air. Hot air rises because it is less dense(less heavy) than colder air which sinks. Likewise, the higher you go in elevation, the air pressure falls. In fact, older altimeters, devices that measure altitude, were based on this fact and were nothing more than scaled barometers.
Barometic pressure is measured in units called inches of Mercury or millibars. Original barometers measured how far air could push a pool of mercury up an empty tube. The average sea-level pressure is 29.92 inches of Mercury, or 1013 millibars. The lowest recorded barometic pressure was 25.69 inches and the highest recorded barometric pressure was 32.01 inches.
The barometer is a fascinating instrument that is an important instrument for studying the weather. A meteorologist would find it very hard to forecast the weather without using a barometer. A barometer can tell whether the air pressure is high, which usually means fair weather, or low, which usually means stormy weather. A barometer can show trends to see whether the air pressure is getting higher which means better weather is on the way or it can show whether the air pressure is getting lower which means stormy weather is on the way.
Because of this, the barometer is the most essential instrument in a home weather station. Any backyard weather hobbyist would do well to make sure that his home weather station, including electronic weather instrument stations, has a barometer built-in.
Electronic weather barometers are great because they don’t have to be calibrated like other weather instruments. They also are much more accurate for accurate readings and can allow you to take readings from the comfort of your own home, without going out in stormy weather to find out weather readings. Better home weather stations also keep detailed records of barometric pressure readings.
