You could slap a GPS receiver in a digital watch and have something that still worked when you went on vacation. Gears are cool and all, but I think they passed the typewriters and cassette tapes but for rich people mark several miles back.This is mostly due to the fact that times for sunup and sundown are specific to latitude, which means every watch is basically a custom order as you have to make the cams that control the movement of the hands for each individual watch depending on the location desired by the owner. I'd assume the same latitude specificity applies to the length of day indication as well; you'd need a different disk for each latitude (the indication of sunrise and sunset on the VC Celestia changes thanks to the rotation of a bi-colored disk hidden behind the slit on the dial).