An ATM, or atmosphere, is a unit of measurement used to express pressure. One atmosphere is defined as the average pressure at sea level on Earth, which is approximately 101,325 pascals. This measurement helps scientists and engineers understand how gases behave under different conditions, such as in weather systems or during chemical reactions. In addition to its use in science, the concept of ATM is important in various fields, including meteorology and aeronautics. For example, as an aircraft ascends, the atmospheric pressure decreases, which affects the performance of the aircraft and the behavior of the air around it.