The original versions of The Wonder Clock came from Germany (you can read more here).
Although this plastic one from Sam Dalal looks pretty cheap it works very well and would certainly fool anyone not in the know.
Effect: This is a prop that can be used to perform an amazing mental effect.
The performer can correctly guess the time set on the miniature clock by any member of the audience, even though the clock face is entirely covered by a sliding opaque cover.
Measuring only 4″ long, by 2.75″ wide, and 0.75″ thick, this eye catching prop can be carried in your pocket, ready for use any place, any time.
Easy to do, mechanical in working and comes complete with instructions.
(Notice: Includes: Printed Instructions.)( Post Source: martinsmagic.com - click for details )