Petty averages

are sundry small charges, which occur regularly, and are necessarily defrayed by the master in the usual course of a voyage; such as port charges, common pilotage, and the like, which formerly were, and in some cases still are, borne partly by the ship and partly by the cargo. In the clause commonly found in bills of lading, "primage and average accustomed," average means a kind of composition established by usage for such charges, which were formerly assessed by way of average.- Arnould.

See under Average.