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In-house manufacture caliber · caliber Omega Cal. 8900: Co-Axial Master Chronometer automatic, 25,200bph, 60h PR, 39j; METAS-certified, anti-magnetic to 15,000 gauss; used in Aqua Terra and De Ville · 60h power reserve (2.5 days) · see-through caseback

Also uses Omega Cal. 8900

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Omega Seamaster Aqua Terra, 41mm Ref. 220.10.41.21.03.001, black dial, steel case
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Seamaster Aqua Terra
Medium-large: suits wrists 6.5 in+ (16.5 cm+)
41 mm case. Wears confidently on average to larger wrists. May overhang on slender builds.

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Authentication

Both the dial-side sapphire window and the caseback must be clear; any Hour Vision with a misaligned or offset dial window has had the movement incorrectly serviced or replaced.

Known issues in the market
  • The through-dial sapphire window must be exactly centered on the movement architecture below it; any offset indicates incorrect movement seating.
  • Both sapphire crystals (dial side and caseback) must be scratch-free; any scratching on the dial-side crystal requires crystal replacement before purchase.
  • The exhibition caseback shows the full Co-Axial movement; confirm Cal. 8900 architecture with the Co-Axial fork visible.
AreaWhat to checkWhat is correctRed flag
crystalDial-side sapphire window alignmentWindow exactly centered over the movement with equal margins on all sidesAny offset or asymmetric margin around the window indicating incorrect movement seating or replacement
casebackExhibition caseback clarityClear scratch-free sapphire caseback showing Co-Axial movement architectureScratched caseback crystal; movement visible through caseback not matching Cal. 8900 Co-Axial architecture
movementCal. 8900 Co-Axial escapementCo-Axial three-arm lever fork visible through both caseback and dial windowStandard lever escapement without Co-Axial fork; any caliber designation other than 8900
Common legitimate replacements
  • Dial-side sapphire windows are occasionally scratched on preowned examples; any scratch requires crystal replacement, adding to service cost.
  • The exhibition caseback on the Hour Vision is a double-sealed system; inspect the caseback gasket for signs of repeated opening.
Expert resources: Omega.com De Ville Hour Vision documentation. Omega Forums for Cal. 8900 dial-window alignment reference images.

Authentication guide

Last reviewed June 2026

The Hour Vision 41mm has an open-dial skeleton architecture. The co-axial escapement visible at the 6 o'clock dial aperture and the balance wheel visible at 12 are the definitive authenticity elements. The display caseback confirms the caliber.

Known reproduction risks

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MEDIUM

Non-functioning or incorrectly positioned movement apertures

  • Standard lever escapement geometry visible at the 6 o'clock aperture instead of a co-axial wheel
  • Apertures present but no movement visible behind them -- decorative plates rather than genuine windows
  • Balance wheel missing or static when the watch is running

Dial variants by era

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EraDescriptionIdentifiers
2017 to present (cal. 8900)Open-architecture dial with sapphire windows showing the movement. Co-Axial escapement wheel at ~6 o'clock on the dial face. Balance wheel at 12 o'clock. Display caseback. Black, silver, and blue colorways. Applied indices on the outer chapter ring.
  • Co-Axial escapement wheel visible at ~6 o'clock on the dial side
  • Balance wheel visible through the 12 o'clock aperture
  • Display caseback with decorated movement bridges
  • "Co-Axial Master Chronometer" designation
  • Polished steel bezel
  • Applied hour indices on the outer dial ring

Service part flags

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Dial-side aperture alignment

Original: The sapphire dial apertures must align precisely with the movement components they reveal. The co-axial wheel should be centered in its aperture and the balance wheel should be fully visible in the 12 o'clock window.

Replacement tells
  • Movement component not centered in its aperture -- movement has shifted during service
  • Aperture partially obscured by the dial structure
  • Scratch marks on the inner surface of the sapphire aperture from incorrect dial clamp use
Display caseback

Original: Sapphire display caseback with decorated movement. Geneva-wave finishing on movement bridges. Omega-engraved or skeletonized rotor on some variants.

Replacement tells
  • Solid caseback replacing the display caseback
  • Plain-finished bridges visible through the caseback
  • Rotor without Omega engraving where decoration is expected

Case back markings

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2017 to present
  • Display caseback -- caliber visible through sapphire: Cal. 8900
  • "OMEGA" on the movement bridges
  • Case reference and serial number on the case band

Movement tells

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  • Cal. 8900 is automatic with 60-hour power reserve. The balance wheel visible at 12 should oscillate smoothly at 25,200bph.
  • Any watchmaker service on the Hour Vision should preserve the dial aperture alignment. Post-service inspection should confirm both apertures remain correctly centered over their movement components.
Sources: Omega De Ville official; Hodinkee De Ville Hour Vision review.

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