Figuring out how far north or south you are, even when at sea, is fairly easy. You just need to find the height of the sun at noon (i.e., when the sun is due north or south of your position) and apply a corrective factor based on the time of year. That is, all that's required to determine your latitude is a compass, a sextant, and a single table--all of which sailors would have had easy access to. Historically, there have been two forms of attempted solution to this problem: In the modern-day era of GPS and radio signals broadcast by atomic clocks, this is almost never an issue.