The Arnold and Son HM Double Hemisphere Perpetual Moon has a 42mm case made of 18K rose gold. Just like the rest of the Royal Collection, this new iteration features the classical case with double-stepped lugs and sword hands, with a double finishing (polished on one side and brushed on the other). The Arnold and Son HM Double Hemisphere Perpetual Moon has a rather simple display and the moon-phase excepted, only displays the hours and minutes. However, its movement isn’t that simple. The Calibre A&S1512 features a double barrel for 90 hours of power reserve and is finished with manually chamfered bridges with polished edges, fine circular graining, and Côtes de Genève rayonnantes, blued screws with polished and chamfered edges.
On the reserve side of the movement, we can see an intriguing dial, also displaying the phases of the moon. It has no other goal than to help the wearer to set the right position of the moon on the dial side. The moons on the front have no track and in order to perfectly adjust them, Arnold and Son cleverly added a second and precise sub-dial on the case back, with a scale and the representations of all the different phases of the moon.