In 1965, Denniston was hired by
Kelly Services, an employment agency. She was assigned to
MIT Instrumentation Lab (now Draper Laboratory), and was hired directly by the lab within a few months of starting. Denniston worked as a
keypunch operator, taking the developed source code and entering it onto the
keypunch cards. According to Denniston: I punched the cards that eventually were turned into the program for the guidance system for the Apollo project. Punching cards is punching cards whether you’re in an insurance company or working on the Apollo project. The programmers would give me 11-inch by 17-inch sheets of paper. They would write the program in blocks. My job was to keypunch it onto the cards. Remember, direct access to computers didn’t happen back then. Denniston was known for catching errors made by the programmers, such as a missing symbol or closing parentheses. At the time, the punchcards would be processed overnight, and an error could waste the entire run. Denniston left MIT after two years due to lack of opportunity for advancement. She cited training someone who eventually became her boss in the department. She was told that they needed someone to come in for support, no matter the time of day. She was the mother of two at the time, and felt this was the reason she was
overlooked for advancement: "I think looking back that was the only time I felt being a woman was against me, so to speak". == Later career ==