What is the primary function of the pressure gauge on a fire extinguisher?

The primary function of the pressure gauge on a fire extinguisher is to determine whether it is charged. The pressure gauge provides a visual indication of the internal pressure of the extinguisher cylinder, which directly correlates to whether the extinguisher is ready for use. A gauge that shows the needle within the green zone indicates that the extinguisher has an adequate pressure to function effectively. If the gauge needle is in the red zone, it signifies that the extinguisher may be undercharged or overcharged, and it could be ineffective in an emergency situation.

Other options touch on aspects that are not the primary purpose of the pressure gauge. For instance, while the color of the extinguisher may be relevant for identifying the type of fire it can address, it is not indicated by the pressure gauge itself. Similarly, safety ratings are not displayed through the gauge, and the weight is not measured by it; weight considerations would involve different scales and specifications unrelated to the pressure level indication.