As an extreme example, imagine that you placed a sundial somewhere in the Arctic Circle on the summer solstice. On that day, you marked the hours along the shadow cast by the sundial. Throughout the rest of the year, those marks would become increasingly inaccurate. That is because of the tilt of the Earth in relation to its orbit—the same reason why the poles have periods when there is no sunset and other periods when there is no sunrise. To compensate for those factors and daylight savings time, Redditor Onemywaybackhome built this self-correcting sundial.
Onemywaybackhome doesn't say where they live, but it probably isn't near one of the poles. Still, every location on Earth is subject to changes in daylight throughout the year. Most of the time, the sun isn't actually at its highest point when your clock reads noon. To calculate the moment at which the sun will be at its highest point, you need to know your exact location (longitude and latitude) and the date. With that information, you can determine the difference between solar noon (when the sun is at its highest) and noon on your clock. This sundial performs that calculation and uses the difference to rotate its dial to the most accurate position for the day.
That dial, as well as the frame that holds it in place, is laser-cut. The dial rides on 3D-printed gears and a small stepper motor rotates those gears. An Arduino Nano board controls the stepper motor. The Arduino makes its adjustments according to solar noon calculations. Onemywaybackhome hardcoded the device with the sundial's location, but the Arduino still needs to know the date to complete its calculations. To figure out the date, it uses a real-time clock (RTC) module. There is something very funny about using a digital clock to adjust a sundial, but that was the most sensible solution in this case. Power comes from a battery that is charged by a solar panel, so at least the device is still solely reliant on the sun.