But in some of its aspects Japanese traditional bookkeeping was curiously similar to the double entry system. In Nakai’s bookkeeping method, as Professor Ogura notes, a duality of entry was maintained throughout the entire system. All entries were made in pairs in different books and checked against each other and marked with a stamp, For instance, the total of cash sales entered in the sales book was balanced with a cash receipts entry in the cash book. In the same way all entries were balanced and marked one by one continuously through all related account books to: the final end, the annual inventories. These provided a proof of entries and calculations and also substantiated the duality of entries maintained throughout the whole system. The Tanabe family system provided for three semi-annual statements, one statement of assets and liabilities, and two income statements respectively showing (1) net results by comparing opening with closing balances of assets and liabilities6 and (2) summaries of revenues & expenses and operation results. One was prepared by “inventory method” and the other by “derivation method.’’7 Tanabe businessmen called those “double-sided accounts.”