
'Viking sunstone' found in shipwreck - zoowar
http://www.bbc.co.uk/news/world-europe-21693140
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drallison
_Testing a similar crystal, the scientists proved that by rotation it was
possible to find the point where the two beams converge - indicating the
direction of the Sun._

 _They say it works on cloudy days, and when the Sun has set._

Hard to see how it could work when the Sun has set.

