Abstract
This paper examines the Profit on merchandise accounts (a forerunner of the income statement) in a sole proprietorship in Pisa that officially operated between 1386 and 1392, but took several months to finally end its activities, which it did in 1393. The Profit on merchandise account was where the balance on each goods account was transferred when all the items recorded in it were sold. The principal contribution of this paper is the identification of a unique approach to medieval product costing that ensured indirect expenses on merchandise were recovered from customers when sales took place, while earning an average return of over 10 percent on those costs. It also highlights the problems encountered when working with archival material that has deteriorated over time; and presents a research method that reconstructs missing data using the trail to original entries and contra entries recorded in double entry.