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A barometer is a scientific instrument that is used to measure air pressure in a certain environment. Pressure tendency can forecast short term changes in the weather. Many measurements of air pressure are used within surface weather analysis to help find surface troughs, pressure systems and frontal boundaries.
The first devices used to measure weather phenomena were the rain gauge, the anemometer and the hygrometer. The 17th century saw the development of the barometer and the Galileo thermometer while the 18th century saw the development of the thermometer with the Fahrenheit and Celsius scales.
This corresponds to 751.16 mm, [9] so that on the present-day definition, this boiling point is 99.67 degrees Celsius. [10] 1743 — Jean-Pierre Christin had worked independently of Celsius and developed a scale where zero represented the melting point of ice and 100 represented the boiling point but did not specify a pressure. [8]
The United Kingdom, through voluntary and mandated laws, has metricated most of government, industry, commerce, and scientific research to the metric system; however, the previous measurement system (Imperial units) is still used in society. Imperial units as of 2024 remain mandated by law to still be used without metric units for speed and ...
The squeeze-film pressure sensor is a type of MEMS resonant pressure sensor that operates by a thin membrane that compresses a thin film of gas at high frequency. Since the compressibility and stiffness of the gas film are pressure dependent, the resonance frequency of the squeeze-film pressure sensor is used as a measure of the gas pressure.
Where these units also had a standard, legally defined definition, such as given in a weights and measures act, this was known as the statute measure. [5] So a land area might be given as 24 acres—statute measure, to clarify that it was the acre defined in statute, rather than a customary acre of a different size, that was being used. [5]
Atmospheric pressure, also known as air pressure or barometric pressure (after the barometer), is the pressure within the atmosphere of Earth. The standard atmosphere (symbol: atm) is a unit of pressure defined as 101,325 Pa (1,013.25 hPa ), which is equivalent to 1,013.25 millibars , [ 1 ] 760 mm Hg , 29.9212 inches Hg , or 14.696 psi . [ 2 ]
Pressure as a function of the height above the sea level. There are two equations for computing pressure as a function of height. The first equation is applicable to the atmospheric layers in which the temperature is assumed to vary with altitude at a non null lapse rate of : = [,, ()] ′, The second equation is applicable to the atmospheric layers in which the temperature is assumed not to ...