I've always thought this was remarkable

Ancient Greek Computer Had Surprising Sun Tracker

The world’s oldest astronomical calculator is famous for having intricate gear systems centuries ahead of their time. But new work shows the Antikythera mechanism used pure geometry, as well as flashy gears to track celestial bodies’ motion through the heavens.

The device, a 2,000-year-old assemblage of gears and wheels that matched 19th century clocks in precision and complexity, was salvaged from a shipwreck off the Greek island of Antikythera in 1901.

Called the Antikythera mechanism, the machine gracefully kept track of the day of the year, the positions of the sun and the moon, and perhaps the other planets. It also predicted eclipses and kept track of upcoming Olympic games.

Now, due to some new research, it turns out it uses precise geometry to allow for irregularities in apparent speed of the Sun's transit across the heavens due to Earth's elliptical orbit.