Hafvilla: A Note on Norse Navigation, G. J. Marcus, Speculum, Vol. 30, No. 4 (Oct. 1955), pp. 601–05, Published by: Medieval Academy of America, https://www.jstor.org/stable/2849616Archived 30 January 2020 at the Wayback Machine (accessed 2 November 2011).
Hafvilla: A Note on Norse Navigation, G. J. Marcus, Speculum, Vol. 30, No. 4 (Oct. 1955), pp. 601–05, Published by: Medieval Academy of America, https://www.jstor.org/stable/2849616Archived 30 January 2020 at the Wayback Machine (accessed 2 November 2011).