What does the black hand of the duplex air gauge indicate?

The black hand of the duplex air gauge specifically indicates the brake pipe pressure. In a train's air brake system, the brake pipe is crucial for transmitting air pressure to the brake cylinders, which in turn applies the brakes on the train. By monitoring the black hand, train operators can assess the pressure within the brake pipe, ensuring that it is at the correct level for safe and effective braking. This information is vital for managing the train's braking system, especially during operations that require precise control over speed and stopping distances.

Understanding the gauge readings helps operators respond appropriately in various situations, such as when making a stop or adjusting speed. Monitoring brake pipe pressure is one of the key aspects of ensuring operational safety when handling train operations.