As I understand it, part of the problem is that this was a ledger-based system - just a really terribly implemented one which gave the sub-postmasters who were

As I understand it, part of the problem is that this was a ledger-based system - just a really terribly implemented one which gave the sub-postmasters who were liable for any shortfalls terrible visibility into what the transaction history was, why corrections were being made, whether their own staff could be defrauding them, etc.