A wandering hour complication displays the time by moving a pointer showing the hour across an arc showing the minutes.
The Campani brothers are credited for creating the wandering hour concept in the 1600s in a clock for the Pope. It traditionally consists of a central three- or four-armed cross with a disc or cylinder at the end of each arm which rotates to show the current hour and points to the minutes along an arc-shaped track. The complication is fairly straightforward, as each of the 12 hours is evenly divisible by three or four, so each arm can show the same number of hours. Similarly, the dial is divisible according to the number of arms, so a three-armed system will show the minutes on a 120º track, while a four-armed system uses 90º of the dial.
In modern times, Audemars Piguet is credited for bringing the wandering hours display to market in a watch with their 1991 Star Wheel. Urwerk has exploited the concept to its fullest extent from their first UR-101 watches in 1997 to today's full "Ur-Satellite" line, which uses both three- and four-armed crosses and adds an extendible pointer. Urwerk produced a special wandering hour watch for Harry Winston, the 2005 Opus V, and Arnold & Son recently produced their own as well, the Golden Wheel. In 2011, Parmigiani introduced the Toric Capitole with what they refer to as a "sector time display", a three-arm wandering hours system.