Atmosphere (unit)
An atmosphere (atm) was a unit of measurement for pressure, defined by the force exerted by the weight of air molecules in an atmosphere.

Comparative units of pressure 

When Jonathan Archer chose to interrogate the Osaarian pirate Orgoth for information about the Xindi in 2153, he placed the Osaarian into an airlock and began decompression it at a rate of 0.5 atmospheres per minute until his captive would start talking. He warned Orgoth that he better start soon or "in about forty seconds you won't be able to." ()

The Federation typically measured the atmospheric pressure of planets they encountered by relating to "Earth normal". () The atmospheric pressure of the habitats aboard the Nyrian biosphere vessel, encountered by  in 2373, were kept at an Earth-normal atmosphere or 1 atm. ()

When Mira Romaine became possessed by the Zetarians in 2269, she was placed in the pressure chamber where she was subjected to increased pressure. James T. Kirk ordered it pressure chamber to start at 2 atmospheres, then had it increase 1 atmosphere per second until it reached roughly 3.5 atmospheres, when they were finally forced from her body. ()

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Measurements