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The project was conceived by Danny Hillis in 1986 and the first prototype of the clock began working on December 31, 1999, just in time to display the transition to the year 2000. At midnight on New Year's Eve, the date indicator changed from 01999 to 02000, and the chime struck twice, to ring in the (popular) third millennium. That prototype, approximately two meters tall, is currently on display at the Science Museum in London.

1 Design

The basic design requirements of the clock were:

• Longevity: The clock should be accurate even after 10,000 years, and must not contain valuable parts (such as jewels, expensive metals, or special alloys) which would encourage looting.
• Maintainability: Future generations should be able to keep the clock working with nothing more advanced than Bronze Age tools and materials, if necessary.
• Transparency: The clock should be understandable without stopping or disassembling it; no functionality should be opaque.
• Evolvability: It should be possible to improve the clock over time.
• Scalability: To ensure that the final, large, clock will work properly, smaller prototypes must be built and tested.

Obviously, no clock can have a guaranteed lifetime of 10,000 years, but some clocks are designed with guaranteed limits. For example, a clock that shows a four-digit year date will not display the correct year after the year 9999. With continued care and maintenance the clock could reasonably be expected to display the correct time for 10,000 years.

Whether a clock would actually receive continued care and maintenance for such a long time is debatable. Hillis chose the 10,000-year goal to be just within the limits of plausibility. There are technological artifacts, such as fragments of pots and baskets, from 10,000 years in the past, so there is some precedent for human artifacts surviving this long, although no human artifact has been continuously tended for more than a few centuries at most.

Many options were considered for the power source of the clock, but most were rejected due to their inability to meet the requirements. For example, atomic energy and solar power systems would violate the principles of transparency and longevity. In the end Hillis decided to require regular human winding. This may seem an odd choice, but remember that the clock design already assumes regular human maintenance.

The options considered as sources of timing for the clock included:

• pendulumA gravity pendulum is a weight on the end of a rigid rod, which, when given some initial lift from the vertical position, will swing back and forth under the influence of gravity over its central (lowest) point. A torsion pendulum consists of a body suspe (inaccurate over the long term, and requires lots of ticks)
• balance wheel (even more inaccurate)
• torsion pendulum (potentially slower, but even less accurate)
• water flowA water clock or clepsydra is a device for measuring time by letting water regularly flow out of a container usually by a tiny aperture. History Water clocks were among the earliest timekeepers that did not depend on the observation of celestial bodies. (inaccurate and wet)
• solid material flow (inaccurate)
• daily temperature cycle (unreliable)
• seasonal temperature cycle (imprecise)
• tidal forceTidal force due to variations in gravity For a given gravitational field, the tidal acceleration at a point with respect to a body is obtained by vectorially subtracting the gravitational acceleration at the center of the body from the actual gravitationas (difficult to measure)
• Earth's rotating inertial frame (difficult to measure accurately)
• stellar alignment (unreliable because of weather)
• solar alignment (unreliable because of weather)
• atomic oscillator (not transparent, difficult to maintain)
• piezoelectric oscillator (not transparent, difficult to maintain)
• atomic decay (difficult to measure precisely)
• wear and corrosionCorrosion is the destructive reaction of a metal with another material, e. oxygen, or in an extreme pH environment (either acidic or basic). The corrosion product is a mix of oxide and salts of the original metal. Corrosion is the primary means by which m (very inaccurate)
• rolling balls (very inaccurate)
• diffusionThis article is about the physical mechanism of diffusion. For alternative meanings, see diffusion (disambiguation). Diffusion is the spontaneous spreading of something such as particles, heat, or momentum. The phenomenon is readily observed when a drop o (inaccurate)
• tectonic motionThe concept of continental drift was first proposed by Alfred Wegener. In 1912 he noticed that the shapes of continents on either side of the Atlantic Ocean seem to fit together (for example, Africa and South America). Benjamin Franklin and others had not (difficult to predict and measure)
• orbitFor other meanings of the term "orbit", see orbit (disambiguation In physics, an orbit is the path that an object makes, around another object, whilst under the influence of a source of centripetal force, such as gravity. History Orbits were first analyseal dynamics (difficult to scale)
• tuning fork (inaccurate)
• pressure chamber cycle (inaccurate)
• inertial governor (inaccurate)
• human ritual, (too dependent on humans).

A suitable timing source must be reliable, meaning that it wouldn't easily become stopped. But it must also be accurate. Hillis concluded that that no single source of timing would meet the requirements, so the clock will use an unreliable but accurate timer to adjust an inaccurate but reliable timer, creating a phase-locked loop. Specifically, the current design uses solar alignment to adjust a slow mechanical oscillator, based on a torsional pendulum. The combination can, in principle, provide both reliability and long-term accuracy.