Mercury: The mercury barometer, sometimes called a stick barometer, was the first to be invented. It uses an open tube system with a pool of mercury that rises and falls with pressure changes. They only work at an altitude up to 1,000 feet. [3] X Research source Aneroid: The aneroid barometer doesn’t use any liquids. It uses a small box made from beryllium and copper that expands or contracts based on pressure changes. These motions cause mechanical hands to move pointing towards the current air pressure. Electronic: Electronic barometers are a little more complicated to understand, but they employ sensors and strain gauges that cause changes in voltage that can be converted to a display of pressure for the user.
Setting your barometer to your location will take into account differences in pressure caused by the altitude of your location. The factory setting for aneroid barometers is at sea level, but if you don’t live at sea level, you will need to calibrate it. [4] X Research source
If you are using a mercury barometer, you will have to use a conversion for your readings. Digital barometers have sensors to calibrate altitude automatically.
Well-sealed and air-conditioned rooms are not as affected by changes in air pressure, so avoid these rooms if possible. Avoid a location that is exposed to direct sunlight as the temperature changes can affect the readings. Hang the barometer away from drafty locations, like near a door or a window. Air pressure is too variable in these locations. [5] X Research source
If you have a mercury barometer, the mercury should rise to the top of the tube and produce an audible “tick” sound that you may also feel. The tube should fill with mercury. If you have an aneroid barometer, the indicator hand should rotate clockwise around the dial. If your barometer fails this test, you may need to have it professionally serviced and re-set before you can count on its accuracy. However, most barometers can last years with no servicing.
The set hand will serve as a reference that allows you to easily tell if the pressure is steady, rising or falling. Remember, this hand will only be present on an aneroid barometer. If you have an electronic barometer, you can simply check the reading. If you have a mercury barometer, you will need to correct for altitude if you’re above sea level.
Find your elevation and then use the chart to find the relevant correction factor. Add the correction factor to the reading on the barometer. This reading should match the reading of the local weather service. If you are at an elevation of over 1,000 ft, mercury barometers do not work. [9] X Research source
If using an aneroid or mercury barometer, gently tap the face of the barometer to release any pressure changes stored in the mechanisms. Take the reading after the needle or mercury has stopped moving. For the aneroid barometer, move the set hand if the pressure has changed so the next time you check it will be obvious what direction the air pressure is going.
Do not expect large changes in the movement of the needle. Daily changes are usually between 0. 02 and 0. 10 of an inch using the barometer scale. Variations are dependent upon location and altitude. Take frequent readings (every few hours) and plot them on your graph.
If the reading is over 30. 2 inches of mercury and falling rapidly, this indicates cloudy, but warmer weather. If the reading is between 29. 8 and 30. 2 inches of mercury and falling rapidly, rain is most likely on the way. If it’s under 29. 8 inches of mercury and falling slowly, rain is likely; if it’s falling rapidly, a storm is imminent.
Readings over 30. 2 inches of mercury that rise indicate that the weather will continue to be fair. Readings between 29. 8 and 30. 2 inches of mercury that rise indicate that the weather will remain whatever it presently is. Readings under 29. 8 inches of mercury that rise indicate that the weather is clearing, but will be cooler.
A strong high pressure system is around 30. 4 inches of mercury. Anything above 30 is considered high pressure. [15] X Research source A typical low pressure system is around 29. 5 inches of mercury. Anything below 29. 9 is considered low pressure.
