In 1494, Luca Pacioli was the first to describe the accounting statements that he called the "bilancio del libro" and "summa summarum" While the "bilancio del libro," or trial balance, never raised doubts as to its usefulness, the obscure interpretation of the summa summarum in the treatise and the inclusion of both statements by Pacioli led to varied perceptions of the value and meaning of this section of his treatise. This paper presents the results of many years of research in the archives of the merchant of Prato, Francesco Datini's companies between 1363 and 1410. It reports the finding of the earliest known example of a "bilancio del libro" inside the Ledger in 1395 when, in one accounting cycle, the company simultaneously formed both documents. The bilancio del libro served as a trial balance and the summa summarum was used as a statement to be transmitted to the head office. The research method employed was logical and analytical modeling.