This mantel clock is a 1960's attempt at a digital display, before electronic digital displays were commonplace.
The numerals are on 3 plastic drums that are rotated by a small electric motor.
The clock movement is a conventional balance wheel and pin pallet escapement. Once per minute electric contacts are closed and the spring that powers the clock is rewound by an electric motor which also advances the display by one minute.
Detail of the movement.
Detail of the rewind mechanism.