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Meteorology and Weather
Atmospheric Sciences

What instrument measures atmospheric pressure?


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December 15, 2017 3:45AM

The instrument, most commonly used in science, is a barometer.

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The word, Barometer, is derived from baro, meaning weight or pressure, and meter, meaning measuring device.

Barometers can be either analog or digital. The traditional analog barometer is known as an aneroid barometer. These are the round chrome or brass type that you would normally see on the bridge of a ship, many times accompanied by clock, temperature, and/or humidity gauge.

For an accurate and reliable aneroid barometer, you should expect to pay $249.00 or more. For aneroid barometers, accuracy and reliability will wane incrementally below that price. The cost of scientific instruments, including barometers, are directly tied to accuracy and reliability. In some cases, however, as you go up in price, accuracy will remain stable but quality of materials and craftsmanship will drive the price upwards (i.e. use of thick solid brass or chrome).

Digital barometers emulate the results achieved from an aneroid barometer (sometimes called a "nautical barometer). Their accuracy varies wildly and is not necessarily tied to price. For example, the barometers, in even the most reasonably priced (under $100.00) La Crosse Weather Stations, are exemplary performers. Anecdotal observations over many years show that the La Crosse variance from NIST traceable, accurate weather stations has been minimal (±.01). Other inexpensive manufacturer's products have nowhere near this steady and predictable tolerance. And many are as much as .06-.10 or 2-3mb off after initial calibration.

All barometers are not the same. Most have elevation limitations. With the Weems & Plath barometers, specific elevations are designated by each individual product. So, be sure to probe for this information before you buy. Some barometers can be upgraded for high elevation use. But this is relatively expensive, and generally for those barometers to be used in terrain of 5,000ft.

Digital barometers can have the same limitations. Again, be careful when you purchase. We are not aware of any low cost digital that will function correctly over 5,000-6,000 ft elevation. For high altitudes, or if you're a stickler for accuracy, you must consider the Davis, RainWise, WeatherHawk, or Columbia Weather Systems. Do not rely on any barometer above 5,000-6,000 ft for mission critical or safety applications, unless you are absolutely certain of its well defined and guaranteed specifications. Remember that as you begin to challenge the stated limitations of any scientific device, your inaccuracies will almost certainly increase as you approach the stated threshold. For example, a stated 6,000 ft elevation limit may function perfectly well up to 4,000 ft. Then, possibly a gradual fall-off in accuracy between 4,000-5,000ft. But then a rapid and possibly logarithmic increase in error percentage over 5,000ft. This is just an example and not meant to be a basis for calculating decreasing accuracy in any scientific instrument.

The original analog barometer was the water ball. This instrument featured a glass reservoir at its bottom that fed into a narrowing tube that protruded upwards. As atmospheric pressure increased, the water was driven upwards into the tube, to indicate fair or improving weather conditions. Conversely, as the air pressure dropped, the water level in the tube fell, to indicate a change to more inclement weather. As the water level fell even lower in the tube, it became a more urgent indicator of impending foul weather.