They used the best 1940's equivalent: IBM card tabulators. This is discussed at some length in Surely You're Joking, Mr. Feynman. My favorite part: "When I

They used the best 1940's equivalent: IBM card tabulators. This is discussed at some length in Surely You're Joking, Mr. Feynman. My favorite part: "When I went back to work on the calculation program, I found it in a mess: There were white cards, there were blue cards, there were yellow cards, and I started to say, "You're not supposed to do more than one problem --­­ only one problem!" They said, "Get out, get out, get out. Wait ­­-- and we'll explain everything." "So I waited, and what happened was this. As the cards went through, sometimes the machine made a mistake, or they put a wrong number in. What we used to have to do when that happened was to go back and do it over again. But they noticed that a mistake made at some point in one cycle only affects the nearby numbers, the next cycle affects the nearby numbers, and so on. It works its way through the pack of cards. If you have fifty cards and you make a mistake at card number thirty­-nine, it affects thirty-­seven, thirty-­eight, and thirty-­nine. The next, card thirty-­six, thirty­-seven, thirty-­eight, thirty­-nine, and forty. The next time it spreads like a disease. "So they found an error back a way, and they got an idea. They would only compute a small deck of ten cards around the error. And because ten cards could be put through the machine faster than the deck of fifty cards, they would go rapidly through with this other deck while they continued with the fifty cards with the disease spreading. But the other thing was computing faster, and they would seal it all up and correct it. Very clever. That was the way those guys worked to get speed. There was no other way. If they had to stop to try to fix it, we'd have lost time. We couldn't have got it. That was what they were doing. Of course, you know what happened while they were doing that. They found an error in the blue deck. And so they had a yellow deck with a little fewer cards; it was going around faster than the blue deck. Just when they are going crazy ­­ because after they get this straightened out, they have to fix the white deck ­­ the boss comes walking in. "Leave us alone," they say. I left them alone and everything came out. We solved the problem in time and that's the way it was."