Suppose a merchant in country A has dealings with an agent in country B. The indebtedness between the merchant (principal) and his foreign correspondent (agent) has to be settled in terms of B's currency. Fluctuations in the exchange rate give rise to gains or losses, borne by the merchant. This paper discusses one accounting treatment (in the principal's ledger) of the dealings between domestic principal and foreign agent. It also considers the treatment where the merchant serves as agent for a foreign principal. The discussion is illustrated by references to two 15th century Italian ledgers and to passages in several treatises on bookkeeping and accounts published in the period 1400 to 1800.