> But I grew up in a world where computers do all of the math, and it always looks to me like it's violating the Don't Repeat Yourself principle. If you say the

> But I grew up in a world where computers do all of the math, and it always looks to me like it's violating the Don't Repeat Yourself principle. If you say the same thing in two different places, one of them is always going to be wrong. This is wrong on a couple of levels. In your understanding do RAID disk arrays and backups violate “the Don’t Repeat Yourself principle”? Is one of the copies of the data guaranteed to be wrong? Do data backups duplicate data because of pre-modern thinking? But on another level it’s irrelevant, because in double-entry bookkeeping, there is no duplication of information. If you buy an apple for a dollar, your journal entry will mark a dollar out of cash — which is true because you now have 1 less dollar — and a dollar against your “Food” expense account — which is true because the thing you just spent a dollar on was food. If you took away either entry, you would be losing information. The fact that both entries have to balance isn’t because of duplication, it’s because the same dollar can't exist in more than one place at a time, which is axiomatically true regardless of whether you use a computer.