The Antikythera Mechanism was a portable (laptop-size), geared mechanism, built ca. 150–100 BCE, which calculated and displayed, with high precision, the movement of the sun and the moon and the phase of the moon for a given epoch. It could also predict eclipses and calculate the dates of the Olympic Games. It had one dial on the front and two on the back. Its 30 precisely cut gears were driven by a manifold with which the user could select, with the help of a pointer, any particular epoch. While doing so several pointers were synchronously driven by the gears to show the above mentioned celestial phenomena on several accurately marked annuli. It contained an extensive user’s manual.