In normal service, what should the red hand of the duplex air gauge read?

In typical operational scenarios for trains, the red hand of the duplex air gauge is intended to indicate the air brake pressure within the system. When the train is in a state of normal service, meaning that the air brake system is not actively engaged and the brakes are released, the appropriate reading for the red hand should be at zero. This indicates that there is no air pressure in the brake lines, which is the expected condition for the brakes when they are not being applied.

When the air brake system is functioning correctly and the vehicle is not applying the brakes, the gauge should show a reading of zero. This allows operators to confirm that the air brake system is properly set up before initiating a journey or when assessing the operational readiness of the train. A reading higher than zero could suggest that the brakes are inadvertently engaged or that there is an issue within the air system requiring attention.