Which methods are commonly used to measure air pressure?

The correct choice identifies two widely recognized units of pressure measurement in the context of scuba diving and atmospheric science. The term "BAR" refers to a metric unit of pressure that is roughly equivalent to atmospheric pressure at sea level. It is used frequently in diving to measure the pressure of the breathing gas in scuba tanks.

"Pounds per square inch" (PSI) is another common unit of measurement that expresses pressure in Imperial units. This unit is often used in North America for various applications, including measuring the pressure in scuba tanks, tires, and other pressurized systems. Both BAR and PSI are practical for divers since they relate directly to the pressure of the air we breathe underwater and the physics involved in diving.

Understanding these units is crucial for divers to ensure that they have an adequate air supply and to monitor their environment safely while underwater. Using the right measurements enables divers to make informed decisions about their dive plans and safety protocols, thus preventing potential accidents related to pressure changes.