NavList:

Doug asked: "What are the chances this 1870 navigator invented the Sumner method on his/her own?"

I have no answer to this question. We don't know if the lines were actually plotted on the chart, or if it were just an estimate of the minimum and maximum latitude possible after many hours of dead reckoning. These observations were made on 31 Oct. The day before no observation is recorded so we may guess that the last (noon) latitude is from the 29th, thus the observed latitude may be some 44 to 45 hours old. Then the prudent navigator, close to the shore, would be extra careful and check different possibilities.

Lars
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