In all these difference methods one is impressed by the number of cards which must be punched by the machine and used only once or twice. ... The newer models of the multiplying punch offer possibilities ... to transfer from one counter to another and to punch progressive totals. With slight modification one of these multipliers might become a remarkable "Difference Engine." — W.J. Eckert, Punched Card Methods in Scientific Computation
(NB "progressive totals" in 1940 were what we would now call "prefix sums"; this technique was already, as Eckert alludes to, exploited by Babbage a century earlier)