There are four types of accounting systems. Manual systems are the most rudimentary, where businesses record transactions, such as a sale, and list them individually in a ledger. With single-entry accounting, companies record transactions once in a single account — either an amount coming in or an amount going out — with no insight into how these transactions affect each other. With a double-entry system, companies connect the dots, recording every transaction twice, as a debit in one account and a credit in another. The fourth type of accounting system is computerised accounting, where an accounting system automates many of these processes.