It's the early 1970s, and students in this university engineering course write their Fortran programs on paper, have them punched onto cards and then hand the decks in to be run, says a pilot fish who was there.

"I was working on a difficult assignment: calculating the area under a curve using Simpson's Rule," fish says. "By putting print statements throughout the code, the student could easily debug the program.

"The problem was that we were charged for however much CPU and printer time was used. Those debugging statements cost printer time and paper, and if too many debugging lines printed, it really added up."

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