Apparently the oldest known Mariner’s Astrolabe has been found!
Known as da Gama’s or Sodré’s astrolabe, it was found in the wreck of the Esmerelda, HERE.
The 3D photography indicated it had scribe marks for measuring the height of the sun, allowing the sailors to calculate their latitude.
This simple instrument was much less complicated than the ones used on land, because of ship movement, and these predate sextants by about 300 years.
When I was a navigator in the 80s and early 90s, we still did cel or celestial navigation as a backup to the inertial navigation systems on the airplane. We were happy to be within 5-10 miles of the actual position due to bouncing around and the time it took to take multiple measurements 2 minutes apart on different stars or the sun.
HERE is a nice article from Air and Space on a pilot’s use of a similar bubble sextant. With the advent of accurate clocks, good charts, The Nautical Almanac, and the training to plug and chug though the various pages, calculations, declination, etc. You could actually get close enough to home to get a TACAN lock on, where the early mariners were happy to get ‘close’ to what latitude they were on. I cannot imagine how frustrating that must have been to the navigators on those ships!!!