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Spherical moonphase

High confidence

A rotating sphere, one half polished palladium and the other heat-blued steel, showing the moon's phase in three dimensions rather than as a disc behind an aperture. The gearing is quoted as drifting by about a day only after more than a millennium, which is an arithmetic claim following from tooth counts.

Part reference

Brand
De Bethune
Material
Palladium and blued steel hemispheres

Documented variations

Classification

FactoryDocumented as shipped from the factory for this reference and period.PeriodNot original to this watch, but correct for its production period.ServiceFitted by the manufacturer's own service network. Not a defect.AftermarketThird-party part. Affects originality, not authenticity.ModifiedGenuine parts in a configuration the factory did not sell. Affects originality and value, not authenticity.CounterfeitDeceptive reproduction intended to pass as genuine.UnknownEvidence on file does not settle the question.

  • True sphere with contrasting hemispheres

    FactoryProbable

    Whole production

    Three-dimensionality visible from any angle other than straight on, with two distinctly different surface treatments — mirror-polished metal against heat-blued metal — meeting at the sphere's equator.

  • Flat disc or printed moon in the same position

    CounterfeitProbable

    Whole production

    The substitution. A disc reads as flat the moment the watch is tilted, and the surfaces of a printed moon do not differ in the way polished metal and blued metal do.

Open questions

OpenMissing primary sourceMedium

Gearing behind the spherical moonphase accuracy claim

What tooth counts drive the spherical moonphase, and do they support the quoted accuracy of roughly a day's drift over a millennium?

Scope The same gap the catalog records for the Arnold & Son Perpetual Moon, and answerable the same way: the accuracy follows arithmetically from the gearing, and the gearing is in principle countable. Recording it would convert a manufacturer's figure into a verified specification.

Documented on these references

Provenance of this record

Sources & Evidence

Primary sourceManufacturer documentation

De Bethune — collection and technical documentation

De Bethune SA

Accessed
2026-08-19

Cited for

This referenceHigh confidence
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Last verified: Not yet reviewed