Timepiece and its display switching mechanism

A display switching mechanism of a portable timepiece, comprising:

• a movable dial plate having symbols representing before-noon hours and symbols representing after-noon hours arranged alternately on a circumferential portion;
• a dial plate formed with a plurality of windows in a circumferential portion thereof for allowing said symbols to be seen through said plurality of windows;
• an operating wheel driven via an hour wheel to make one rotation a day;
• a cam freely rotatable about an axis of the operating wheel, having a larger diameter portion and a smaller diameter portions, rotatable by interaction with said operating wheel;
• a lever for causing said movable dial plate to rotate in a reciprocating motion, said lever being in contact with said cam and operating in correspondence with a rotation of said cam to rapidly shift from said larger diameter portion to said smaller diameter portion on a transition from the before-noon to the after-noon and also to subsequently shift from said smaller diameter portion to said larger diameter portion on a transition from the after-noon to the before-noon;
• a spring constantly biasing said lever to maintain contact between the lever and the cam so that said contact moves from said larger diameter portion toward said smaller diameter portion when said transition occurs from said before-noon to said after-noon;
• and
• a retainer constantly forcing said movable dial plate toward a base plate such that said movable dial plate is rotatable in a reciprocating motion via said lever,
• wherein a 12-numeral display appears when said symbols of said movable dial plate are seen through said windows of said dial plate.