Let me do a crude initial look (pending response form those who actually know about the a.mechanism...) at the question of whether the antikythera mechanism could have been used for navigation. I'll ignore the planets and just do the moon+sun, since apparently they do not understand what the mechanism was doing about planets and anyhow those seem much less useful (especially if you are unaware of the moons of Jupiter, etc, which could have been used as a timekeeping device if you were aware of & capable of observing them, which nobody was until the time of Galileo). Suppose you are on an N-day sea voyage. You want to know your latitude and/or longitude. Apparently the magnetic compass was not in any wide use until about the year 1100 AD, so was not available to ancient Greeks (although there seems to be documentary evidence some Chinese knew the principle much earlier). Also, at that time there were no accurate clocks. But you could observe the angle between the sun & moon in the sky, and also the angle of same to the horizon. If you could accurately predict these, you could infer your longitude. Also, if you could predict angle of sun to horizon at noon ("noon" means max-angle time) versus day-of-year, then you could tell your latitude. The accuracy is limited by (i) prediction accuracy and (ii) angle measurement accuracy. If both are assumed accurate to 1 part in 1000 then you could navigate accurate to about 0.001 earth-circumference, which is 25 miles. That seems good enough to be useful. If 0.0001 accuracy then 2.5 miles. So it it not inconceivable, at least as far as this initial crude look is concerned, that the device could have been intended and used for navigation.