The Hettich mantel clock has a large horizontally rotating balance wheel with a half-period of one second which is suspended on a helical balance spring. The movement is a pin pallet. This example is in a veneered case, but many were made under glass domes.
The clock is powered by a U2/MN1300 dry cell which raises a weighted arm approximately every minute. As the weighted arm falls, a contact is made which causes an electromagnet, horizontally mounted at the top of the movement, to kick the weighted arm up again. There is maintaining power provided by a coil spring.
The balance wheel is suspended on a double wound helical spring, half of which is wound clockwise and half counter-clockwise. Thus, as one part of the spring unwinds, the other winds up and the balance wheel does not move in the vertical plane. It is held in place laterally on a vertically mounted tension wire. There is virtually no friction in this mounting.