Pascal (unit) dB SPL, or 20 µPa. The airtightness of buildings is measured at 50 Pa. The units of atmospheric pressure commonly used in meteorology were formerly the bar, which was close to the average air pressure on Earth, and the millibar. Since the introduction of SI units, meteorologists generally measure pressures in hectopascals (hPa) unit, equal to 100 pascals or 1 millibar. Exceptions include Canada, which use kilopascals (kPa). In many other fields of science, the SI is preferred, which means Pa with a prefix (in multiples of 1000) is preferred. Many countries also use the millibars. In practically all other
Pascal (unit) metre. The unit of measurement called an atmosphere or a standard atmosphere (atm) is . This value is often used as a reference pressure and specified as such in some national and international standards, such as the International Organization for Standardization's ISO 2787 (pneumatic tools and compressors), ISO 2533 (aerospace) and ISO 5024 (petroleum). In contrast, International Union of Pure and Applied Chemistry (IUPAC) recommends the use of 100 kPa as a standard pressure when reporting the properties of substances. Unicode has dedicated code-points and in the CJK Compatibility block, but these exist only for backward-compatibility with some older ideographic