Verge escapement
The Foliot ( trembling leaf; German Waag, Balkenwaag or Löffelwaag ) is part of the oldest, since about 1300 used in a mechanical clock mechanism, with the nearly uniform response is achieved ( cf. regulator ).
It includes in addition to the horizontally disposed Foliot the shaft ( spindle), which rotates with the Foliot, and the two flaps attached to it, which engage between the teeth of the crown wheel ( escapement ). The crown wheel is the fastest rotating wheel of the clock. Its rotation rate their gear. Without inhibition by the Foliot mechanism, the clock would go too fast and unevenly. By radially movable weights the moment of inertia of the beam and thus changed the course of the clock can be regulated.
It was not until the invention of the escapement with Foliot enabled the mechanical clock. Your other components, weight drive, gears and rotating pointer, were previously known.
The roughly back and forth rotated by the drive over the crown wheel and the flap located on the spindle Foliot is not a system with natural frequency capability and can not work isochronous. A clock with Foliot was at best just 15 minutes a day. However, the construction with Foliot laid out the guidelines for the use of a mechanical oscillator whose oscillation period is a constant size under free vibration, and it alone determines the timing of the clock. The Foliot was replaced by a mechanical pendulum mid-17th century.
A variant to the bar was a wheel that unrest was called and not to be confused with the balance, which is a mechanical oscillator with a coil spring and later as the pendulum came into use.