[srmanuel]

Just think 500 years ago with nothing more than dead reckoning circumnavigating the globe

[Boogieman]

Well, they had a little more than dead reckoning. They had compasses, and they had sextants, and a decent knowledge of astronomy. They could determine their latitude, directions, and speed just fine, but longitude was the thing they were basically depending on the Captain/Navigator’s “horse sense” to guess at.

[meadsjn]

Just think 500 years ago with nothing more than dead reckoning circumnavigating the globe

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They could determine latitude for many centuries. Had to wait until the mid 1800s to get longitude. Needed timepieces that could maintain within a few seconds for many months, in spite of motion, temperature, and humidity.