Also called a 'mystery clock', this high quality double-dial regulator with pinwheel escapement made by Berthoud in 1850 would have been suspended in a shop window, with the sweep second hand dial facing out, and a just hands and winding arbor dial facing inward. The crutch goes up through the back of the case to interact with a rod that hangs down from the mounting block above, that can just be seen through the top of the pendulum; there is a beat regulator and crutch pin attached to the bottom of the rod.

This one has enameled dials, and a month calendar on the dial that would have faced into the shop.

Here is a video of my other one, a similar vintage: