[superzamp]

> Does recording it twice

Double entry is (confusingly) not about recording it twice, it's about using a transaction model where the state of N accounts has to be changed in compensating directions within a transaction for it to be valid, N being >= 2.

So depending on how your transaction schema is defined, a double-entry transaction can be written without ever even repeating the amount, e.g.

    {"debit": "cash:main", "credit": "giftcards:1234", "amount": 100}

Making it effectively impossible to represent invalid state change. Things get trickier when N > 2 as classical double-entry tend to _not_ directly relate tuples of accounts directly to one-another and instead relying on a aggregated balancing of the changes to the N accounts at the transaction level, though YMMV between different ledgering systems.