Final answer:
Air brake equipped vehicles must have a supply pressure gauge to measure the pressure of the compressed air in the system.
Step-by-step explanation:
Air brake equipped vehicles must have a supply pressure gauge to measure the pressure of the compressed air in the system. This allows the driver to ensure that there is sufficient air pressure for the brakes to function properly. Additionally, air brake equipped vehicles do not require an air use gauge as the brakes themselves do not consume air in operation.