Sumner's Methods

A process for finding the ship's longitude and place when the latitude is in doubt, by employing two assumed latitudes, one greater and the other less than the latitude by account; then, after the sun has changed its azimuth, observing another time sight and working it twice again, using the same two assumed latitudes as in the first workings. These four positions are marked on the chart and crossed with lines, the pint of crossing indicating the position of the vessel at the time of the first sight.