Electrical with zero reset- to demonstrate the phenomenon of trial and error of acquiring a new motor skill. It consists of a mirror drawing box, impulse counter and stylus. The wooden box has a metallic plate with a star pattern grooved in the middle. Over the metallic plate is hinged a screen and the inside of the lid of the box of the carries a mirror. The box is connected to the mains and the error counter ant the stylus operates through the mirrors.

The screen is placed in such a position that the subject is unable to see directly the star pattern but can see the image in the mirror. The subject is asked to move the stylus in between the grooved star is such a way that it does not touch the metallic part, while looking at the image in the mirror. Whenever the stylus touches the metallic parts the circuit is closed and an error is counted along with a buzzer sound.