What condition of the gauge on a portable oxygen bottle is required for it to be considered usable?

For a portable oxygen bottle to be considered usable, the condition of the gauge must indicate an appropriate level of oxygen pressure. A reading of 3/4 to fully indicates that there is adequate oxygen supply available for use. This level ensures that the oxygen bottle is sufficiently filled and can support any required medical or emergency needs.

In practical terms, having a reading below 3/4 could suggest that the oxygen supply is diminishing, which may not be suitable for critical applications where reliable access to oxygen is necessary. Thus, a gauge reading between 3/4 and fully indicates both safety and readiness for use.