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Movement tier: unclassified · caliber Grossmann Cal. 100.0: in-house manual-wind, 21,600bph, 42h PR; three-quarter plate, hand-beveled and polished; exceptional German Glashütte finishing · 42h power reserve
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

The Atum Pure three-quarter plate chamfers must be hand-beveled; machine-polished chamfers do not meet the Moritz Grossmann stated standard.

Known issues in the market
  • The three-quarter plate Glashütte finishing is the authentication reference; sharp hand-done chamfers under loupe.
  • The Grossmann regulator spring is a house signature visible under magnification.
AreaWhat to checkWhat is correctRed flag
movementThree-quarter plate hand-beveled chamfersSharp hand-done chamfers on three-quarter plate bridges; consistent with Grossmann standardMachine-polished chamfers; uniform finish; does not meet Grossmann stated standard
movementGrossmann regulator springGrossmann regulator spring visible under magnification; house signature presentStandard index regulator replacing Grossmann regulator spring; non-genuine movement
casebackThree-quarter plate Glashütte configurationThree-quarter plate visible through caseback; Cal. 100.0 architectureNon-three-quarter-plate movement; non-genuine movement swap
Common legitimate replacements
  • Crown; Grossmann-signed only.
  • Crystal; sapphire standard.
Expert resources: Moritz Grossmann authorized service; Glashütte regional watchmaker network.

Authentication guide

Last reviewed June 2026

The Atum Pure is the flagship manual-wind dress watch from Moritz Grossmann, built around Caliber 100.0. The defining authentication point is the Grossmann balance: no regulation spring, adjusted by eccentric screws visible through the caseback. The finishing level is Lange-tier Glashütte and should be evaluated accordingly.

Known reproduction risks

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MEDIUM

Misrepresentation as a higher-specification Grossmann variant (gold case sold as steel, or standard model sold as Pure).

  • Date window present when sold as the "Pure" (no-date) variant
  • Case material inconsistent with markings (acid test for gold)
  • Movement finishing below the expected Grossmann standard

Outright fakes are not a documented market issue. Misrepresentation of configuration or case material is the realistic risk.

Dial variants by era

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EraDescriptionIdentifiers
2013 to presentSilver or black lacquer dial. Applied gold or rhodium-plated baton indices with subtle faceting. Small seconds sub-dial at 6. No date on the Pure variant. Gold or steel case.
  • "MORITZ GROSSMANN" at 12, "GLASHÜTTE I/SA" below
  • Applied indices with faceted edges, visible catch light
  • Small seconds at 6 with crosshair or minimal inner track
  • No date window on the "Pure" variant
  • Slim case profile: 11.4mm height

Service part flags

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Balance wheel and regulation system

Original: The Grossmann balance uses eccentric screws for regulation rather than a conventional swan-neck spring or index. Under magnification through the caseback, you will see screws at the rim of the balance wheel rather than a regulation spring on the hairspring.

Replacement tells
  • Conventional index or swan-neck regulation spring visible through caseback (wrong caliber)
  • Balance without visible eccentric screws at the rim
  • Movement without three-quarter plate: Grossmann Cal. 100.0 uses a three-quarter plate across most of the movement
Finishing

Original: Bridges and plates are hand-beveled with polished angles. Screw heads are mirror-polished and blued. The barrel and gear train are held by a three-quarter plate with Glashütte stripes. The visible finishing quality should rival A. Lange at this price tier.

Replacement tells
  • Bridges without beveling or with machine-polished edges only
  • Screw heads without blue hue or with uneven bluing
  • Flat brushed bridges without the characteristic Glashütte stripes

Case back markings

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2013 to present
  • Reference MG-001145 (or variant for material and dial)
  • "MORITZ GROSSMANN" and Glashütte address
  • Caliber 100.0 designation
  • Serial number
  • Case material notation (18k gold or steel)

Movement tells

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  • Cal. 100.0 power reserve is 42 hours. Running short of 36 hours from a full wind needs mainspring inspection.
  • The manual-wind crown should engage the stem cleanly with no slop at winding position or time-setting position.
  • Three-quarter plate condition: any scratching or tool marks on the plate under the caseback is a serious provenance concern on a piece at this price.
Sources: Moritz Grossmann caliber documentation, Caliber 100.0; WatchUSeek Glashütte independents thread.

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