



This model operates on principles very similar to Babbage's original designs, though the constraints of using only standard Meccano parts inevitably mean some aspects of the operation are somewhat different. The model can handle decimal numbers with up to four digits, and up to three orders of differences - similar in scope to the fragment of the original Difference Engine #1 which Babbage actually realized in 1832. There is no reason in principle (other than the limited world supply of 2 1/2" gears and ratchet wheels!) why it could not be extended to arbitrary sized numbers and an arbitrary order of differences. Only two basic mechanisms are involved, those for the addition of individual decimal digits, and for the propagation of carries. The rest is repetition. The machine calculates reliably, producing a result about every 4 seconds - somewhat faster than they can be read off and written down. I have no doubt that if the Meccano of the 1920's had existed 100 years earlier, Babbage would have been entirely successful in his quest. It may be amusing one day to attach a Meccano steam engine to drive the mechanism and therefore realize "computing by steam".



The close-up picture below shows the digit addition mechanism in the foreground, with the carry propagation mechanism behind it. These arrangements are repeated vertically to extend the number of digits and horizontally to increase the number of orders of differences.



