NavList:

David,

       Thanks for positing this. My point really hinged on the idea that methods that required plotting would be a challenge under the conditions of the voyage. That would be more likely be the case for intercept/azimuth LoP's that would generally make use of parallel rulers but perhaps less so for Sumner's method which just connects 2 or more points on a chart. Since the calculation in just the time sight calculation done for multiple assumed latitudes Worsley could have used it if he thought his latitude was sufficiently uncertain.

        I would be interested to know what calculation method does Nicholl's prescribe for obtaining the LHA and hence longitude? Worsley uses a different but equivalent method to that used by Sumner in his book (see attached pdf file),

Death to the Intercept Method!

Regards,

Robin Stuart