The best replacement for sextant is octant.

The best alternatives to sextant are rated as following:
★★★★★  octant
★★★  quadrant
★★  sxt
★  astrolabe
★  sextant

Your alternative for sextant is not listed? Suggest!
Speaking about sextant, one probably shouldn't forget about artificial horizon.

Other search terms related to sextant and their ratings are:
★★★★★ artificial horizon
You have in mind a companion for sextant and it is not yet here? Propose!



Google Trends

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sextant
octant
quadrant