Hammer time: fixing the printer on a vintage IBM 1401 mainframe

Based on the text content of the line you were printing, the sound would change from a "brap" (not many duplicate letters on the line) to a "braaaaaaaaaap" when you had lots of the same character, like when someone used the equal-sign as a section separator between paragraphs.

One location on the belt held a metal flag not a type element, and that was how the electronics knew the start of the type element sequence. One of the fun pranks you could do was to swap a couple of the type elements...

The first part of my career was spent studying green-bar. It's how programs were read, understood, and core-dump-repaired if necessary.

I guess we're lucky things got better online. Saving a lot of trees!