This is a rather rough estimate of burthen, the carrying capacity of a ship, and should not be confused with the much more modern measurement of displacement, which would be considerably higher than the figures in the roll. For a detailed discussion of the meaning of tonnage and burthen in early modern naval terminology, Rodger 1997, pp. xx–xxii Rodger, Nicholas A. M. (1997). The Safeguard of the Sea: 660-1649. New York: W.W. Norton & Company. ISBN978-0-00-255128-1.