When oxygen bottles are full, what does the gauge next to the outside filler port indicate?

The gauge next to the outside filler port of an oxygen bottle indicates the pressure of the oxygen inside the bottle. When the bottle is full, the pressure is typically at or near a standard value based on the type and usage of the oxygen system.

In the context of aviation and medical applications, a pressure reading of 1850 psi is commonly accepted as the full pressure for a typical oxygen cylinder. This value ensures that the oxygen is stored safely and is readily available for use.

Understanding these pressure readings is crucial for instructors and practitioners, as they need to ensure that equipment is functioning properly and that there is enough oxygen available for emergencies or altitude operations. Maintaining and checking the pressure ensures safety and compliance with operational standards.