Imagine the situation - you're due to go on a raid tomorrow, but Bjorn Hammersson won your lodestone in a game of hnefetafl
last night. No magnetic lodestone, nothing to indicate North when you're out of sight of land. How are you going to find your way at sea?
Fortunately, with a nail, a lump of wood and a few spare hours, you can construct a sun compass
(To do this Instructable properly, it is not absolutely
vital to be wearing a Viking helmet, but it helps. It's a long time since mine last came out of the shed