Also referred to as 400 day clocks, the anniversary clock was marketed as a timepiece you wind on your anniversary, or once a year. By the nature of its design, it takes very little power to run the clock. One mainspring fully wound was meant to run for 400 days. Over time though, the spring which unwinds so slowly becomes "bound,"  losing some of its power and the ability to fully unwind. That's why I recommend winding twice a year. These mechanical clocks are no longer produced. While it has a fairly simple movement, if not cared for properly, the thin  suspension spring  that the pendulum hangs from will break. Fortunately for repairmen, the Horolovar Company produced a reference book with hundreds of different clocks by the many different makers. The various suspension springs, which differ in thickness by only thousands of an inch, are still available. The pendulum which rotates back and forth, is mesmerizing to watch, making this clock a favorite for people. While the spring driven clocks are not produced today, clocks made in Germany in the 1950's are readily available. In addition to that, quartz anniversary clocks are very common with numerous different designs to choose from. They are made out plastic versus brass, but they have a similar look.