I'm guessing it's gotta be something related to Fortran. Some seminal book or maybe some reference to the "coding sheets" that people would fill out to have ke

I'm guessing it's gotta be something related to Fortran. Some seminal book or maybe some reference to the "coding sheets" that people would fill out to have keyed in. If your program is long, then you have multiple sheets, so maybe that's where the plural comes from?