Any book which contains the first (or original) record of a transaction is a book of original entry (ba).
A CORNER IN THE OFFICES OF THE PLATT IRON WORKS, DAYTON, OHIO
Any book in which records contained in books of original entry (ba) are assembled, to be transferred later to principal books (a), is an auxiliary book.
Any book used for the purpose of assembling statistical information is an auxiliary book.
The books most commonly used in double entry bookkeeping are: Order Book, Day Book, Cash Book, Journal, Sales Book, Purchase Book, Ledger.
13. Order Book. An Order Book is a book of original entry in which is entered a record of each order or request for the shipment or delivery of merchandise. The record shows the name and address of the customer, the kinds and quantities of goods wanted, and the prices at which they are to be sold.
The ruling of the order book varies according to the nature of the business. A simple form of ruling is shown.