Any increase in redundancy should increase the raw error rate. However, with a credit card check digit or md5sum file the additional data is relatively tiny com

Any increase in redundancy should increase the raw error rate. However, with a credit card check digit or md5sum file the additional data is relatively tiny compared to the data it's responsible for checking, so you're much more likely to catch an error than to introduce a new one. Double-entry bookkeeping, in the traditional sense where you actually record every detail about each transaction separately in two or more journals, is more like a RAID-1 mirror: double the data, so approximately double the raw error rate, and if a discrepancy does turn up you'll have no idea which entry was wrong and which was right. But if you lose a journal outright you can recreate it from the mirror image. So far as I know, most actual "double-entry" accounting software just stores each transaction once in a general ledger. The appearance of doubled entries is all in the UI where it processes the ledger to present a list of transactions from the perspective of a certain account. You still get the benefit that the system won't allow the balance of one account to be increased or decreased without an equal and opposite change in other account(s)—money cannot be created or destroyed[1], only moved around. [1] Unless you're the Federal Reserve. They play by different rules.