In early 1962, weeks before John Glenn's orbital flight, a NASA mathematician named Katherine Johnson was asked to recompute by hand what the new IBM 7090 had already calculated, because Glenn had told mission planners he would not fly unless she personally verified the machine's numbers on paper

You may have read the book or seen the movie “Hidden Figures” about the black women who did the manual computing required by space flight. 

Well, here’s a little more detail about one specific set of calculations Katherine Johnson was asked to do. The engineers fed information into the newly installed IBM computer, to figure out how to manage John Glenn’s flight. 

But he wanted her to recompute them by hand to verify what the computer had spit out. 

It’s another way Johnson contributed that is often overlooked. 

https://spacedaily.com/sd-in-early-1962-weeks-before-john-glenns-orbital-flight-a-nasa-mathematician-named-katherine-johnson-was-asked-to-recompute-by-hand-what-the-new-ibm-7090-had-already-calculated-because-glenn-had/