I’ve just spotted an interesting post from Brad Morris on the fascinating website NavList – which is devoted to celestial navigation: http://www.fer3.com/arc/
It’s all about the difficulties facing Frank Worsley in rating his chronometer before departing Elephant island with Shackleton. This was a crucial operation if he was to have any hope of determining the longitude of the James Caird accurately as they crossed the Southern Ocean heading for South Georgia.
As I recount in Sextant, Worsley had to take a sun sight for this purpose and – thanks to foul weather – only just managed to do so before they set off. But for this method to work reliably it was essential to know the exact position of the place where he was making the observation.
Brad Morris says that there was in fact a good deal of uncertainty in 1916 about the exact position of Elephant Island. Not very surprising, given its remote location, but Worsley’s own account doesn’t mention this – perhaps he was unaware of it? http://fer3.com/arc/m2.aspx/Frank-Worsleys-Sextant-certificate-Morris-may-2014-g27804