Accounting is the process of identifying, measuring and communicating economic information so a user of the information may make informed economic judgments and decisions based on it. Accounting is the degree of measurement of financial transactions which are transfers of legal property rights made under contractual relationships. Non-financial transactions are specifically excluded due to conservatism and materiality principles. At the heart of modern financial accounting is the double-entry bookkeeping system. This system involves making at least two entries for every transaction: a debit in one account, and a corresponding credit in another account. The sum of all debits should always equal the sum of all credits, providing a simple way to check for errors. This system was first used in medieval Europe, although claims have been made that the system dates back to Ancient Rome or Greece.