Abstract: A drive is provided for a rotatably mounted display element which is distinctively colored on opposite sides and having a magnet rotatable therewith defining a magnetic axis transverse to the axis of rotation, a pole piece of reversible permanently magnetizable material, designed so that the reversible field of said pole piece will produce opposite orientations of said display element, a coil for energizing said pole piece. There is provided means for determining from the characteristics of current resulting from voltage applied to said coil whether or not the polarity of said pole piece is being reversed.

Abstract: A disc rotatable to exhibit alternately one of its two faces under the influence of an external magnetic field, has its center of gravity offset with respect to the pivoting plane so as to ensure a positive torque when moving from either of its rest positions under the influence of the said magnetic field.