Original Apple, fully tested main circuit board for the revision 2 models of the 'hockey puck' USB mouse although it is functionally interchangeable with the rev 1 board. The back of the revision 2 board is white whereas the revision 1 board is green on both sides.Since the top case is translucent, this affects the appearance of the mouse. This board includes the button micro switch and the optical sensors and was made by Logitech.