Handling the pressure

Arthur’s control panel was a thing of beauty.
So many switches, so many dials, and so many pretty green lights.
Day after day, Arthur would sit in his chair and whistle a happy tune.
When one of the lights turned yellow, Arthur stopped whistling.
He tapped the bulb a few times, just to see if it would change.
It stayed yellow.
Looking in the manual, a yellow light meant… something… to be… corrected.
So, like all the other yellow lights before it, Arthur got out his marker and colored the lightbulb green.
Arthur’s whistling covered the pressure valve leak nicely.