The vikings only did these voyages in the summer. And followed currents and things. I was reading a new book recently, "Den långa medeltiden" http://www.histo

The vikings only did these voyages in the summer. And followed currents and things. I was reading a new book recently, "Den långa medeltiden" http://www.historia.su.se/publikationer/nya-publikationer/den-l%C3%A5nga-medeltiden-1.243446 http://www.historia.su.se/publikationer/nya-publikationer/de... ("The long middle-ages"). ADDED: English summary http://bolin.su.se/index.php/news/372-new-popular-science-book-den-langa-medeltiden http://bolin.su.se/index.php/news/372-new-popular-science-bo... As a viking navigator, I'd want a sunstone. It would be one of many inputs I would integrate. However, as an armchair expert, I'd be surprised if I required it. :)