IWC’s 45-Million-Year Moon Watch
With its Portugieser Eternal Calendar, IWC is dealing with some big numbers. The perpetual calendar function (showing days, months, and years), for instance, is set up to run without any correction for 400 years (traditional perpetuals need adjustments once a century, if you’re counting).
But the accompanying moonphase indication goes somewhat bigger: It’s calculated to give an accurate representation of the moon’s waxing and waning for 45 million years, by which time it will have deviated by just one day.
That’s enabled by some spectacular mathematics around gear-wheel geometries: For the wheels involved, the team whittled down 22 trillion combinations for the proportions, number, and shape of the teeth to find a solution (using a dedicated computer simulation).
To ensure accuracy to the required micro-tolerances, the gears were made by the LIGA microfabrication process, in which parts are effectively “grown”—built up nano-layer by nano-layer—in the lab through a high-tech photolithographic process. It costs around $210,000, but spread that out over 400, or indeed 45 million years, and this piece becomes far more affordable
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