The mechanical anniversary clock also known as the 400-day clock or torsion pendulum clock is one of the most popular clocks ever invented. Anniversary clocks are recognizable by the decorative balls beneath the dial that rotate one way & then the other. To house the attractive mechanism every style of clock case has been used although perhaps the most endearing is the glass dome. The dials hands & ornamentation have also varied steadily over the last century. Called the anniversary clock because it needed winding only once a year it has carried on into the days of no winding at all.