The Definitive Guide to Business Finance: What smart managers do with the numbers, Second Edition

The power of PCs

With the previous thoughts out of the way, let me get back to the story. My first job was in a bank, operating monstrous adding machines (I also made the tea and fed the canary). I totalled, in the constructive sense, anything that did not move, and some things that did: cheques, share certificates, piles of money.

I learned two lessons. First, do everything in two different ways. If the totals disagree, you have made a mistake. Second, if the error is divisible by nine, it is odds on that you have reversed two digits. For example, if you enter 54 instead of 45, the total will be out by 9 exactly. Try swapping two digits in any number and checking by how much it increases or decreases. The difference is always a multiple of nine. ...