For historical methods, see https://en.wikipedia.org/wiki/History_of_longitude#Methods_of_determining_longitude https://en.wikipedia.org/wiki/History_of_longitu

For historical methods, see https://en.wikipedia.org/wiki/History_of_longitude#Methods_of_determining_longitude https://en.wikipedia.org/wiki/History_of_longitude#Methods_o.... Given the presence of an internet connection, I think it’s easiest to query a time server at midday (detected by detecting the time when the sun is highest above the horizon/shadows are shortest) to get longitude. (Latitude is relatively simple; one can, for example, use a sextant to measure the height of the pole star above the horizon)