John Glenn wouldn't fly until one mathematician rechecked the computer's math

Before his 1962 orbital flight, astronaut John Glenn distrusted NASA's new electronic computers and asked engineers to have mathematician Katherine Johnson hand-calculate his trajectory and confirm the machine's numbers. She spent a day and a half reworking the equations by hand. Only after her figures matched the computer's did Glenn agree to fly.

— Margot Lee Shetterly, Hidden Figures: The American Dream and the Untold Story of the Black Women Mathematicians Who Helped Win the Space Race — William Morrow, 2016
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