Atmosphere (atm)
The atmosphere, symbol atm, is a pressure unit originally based on average sea-level air pressure on Earth, defined as 101,325 pascals. First used in the 19th century for meteorology and engineering, the atmosphere is a convenient unit of measurement for expressing pressure in science, including chemistry, physics, and gas laws. Though largely replaced by SI units in formal texts, it remains widely recognized in academia and industry. Its historical role and practical magnitude sustain its relevance in global pressure measurements.
Bar
The bar is a pressure unit in the metric system, equivalent to 100,000 pascals. It was created in the early 1900s to serve the needs of engineers and industry professionals, especially for measuring pressures in the atmosphere and fluids. While it is not officially a part of the SI system, the bar remains popular in fields such as meteorology, diving, and mechanical engineering because of its convenient scale. For example, normal atmospheric pressure at sea level is close to 1.013 bar. The bar provides an easy-to-use alternative to SI units for everyday applications while still maintaining compatibility with metric measurements.