What is the purpose of the two air pressure gauges on the dashboard of a vehicle with a dual air brake system?

Pick an answer

1. They both show the same reading and exist only because of an older design standard
2. One shows fuel pressure and the other shows oil pressure, unrelated to the brakes themselves or the air tanks
3. One gauge is just a spare in case the other one breaks, and both always read the same value
4. One shows pressure for the primary system and one for the secondary system, so a driver can tell if either has failed

Correct!

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