# Debugging ain't what it used to be

Richard Feynman, talking about speeding up calculations during the Manhattan Project:

A rather clever fellow by the name of Stanley Frankle realized that it could be done on IBM machines. The IBM company had machines for business purposes, adding machines that are called tabulators for listings sums and a multiplier, just a machine, a big box, you put cards in it and it would take two numbers from a card and multiple it and print it on a card. And then there were collators and sorters and so on. So he decided, he'd figured out a nice program. If we got enough of these machines in a room, we would take the cards and put them through a cycle...

We had done things like this on adding machines. Usually you go one step across yourself, doing everything. But this was different—where you go first to the adder, then we go to the multiplier, then you go to the adder, and so on. So he designed this thing and ordered a machine from the IBM company... but it was delayed, always delayed... we worked out all the numerical steps we were supposed to do, that the machines were supposed to do, multiply this, and then do this, and subtract that. And then we worked out the program, but we didn't have any machine to test it on. So what we did, I arranged, was a room with girls in it, each one had a Marchant [a desktop mechanical calculator]. But

shewas the multiplier andshewas the adder, and this one cubed, and so we had cards, index cards, and all she did was cube this number and send it to the next one. She was imitating the multiplier, the next one was imitating the adder; we went through our cycle, and we got all the bugs out. Well, we did it that way.

Taken from his talk, "Los Alamos from Below", as reproduced in the book *The Pleasure of Finding Things Out*.