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Movement tier: unclassified · caliber Maurice Lacroix Cal. ML187: in-house automatic with mystery seconds, 21,600bph, 40h PR; used in Masterpiece Seconde Mystere; seconds hand appears to float · 40h power reserve
Large case: suits wrists 7 in+ (18 cm+)
43 mm case. A bold, statement-size wear. Best suited to larger wrists where the case sits flush.

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Authentication

Mystery seconds must move while the movement is running; non-moving seconds with a running movement means the mystery mechanism has failed.

Known issues in the market
  • The mystery seconds drive is the most service-sensitive part of Cal. ML187; any ML187 with non-moving seconds while the movement runs requires specialist service.
  • The off-axis transmission driving the mystery seconds is delicate and should only be serviced by specialists familiar with the caliber.
AreaWhat to checkWhat is correctRed flag
dialMystery seconds functionSeconds hand moves continuously while movement is running; floating appearance with no visible connectionNon-moving seconds with movement running; mystery mechanism failure
casebackCal. ML187 architectureML187 in-house movement with mystery seconds transmission architecture visibleNon-in-house movement; movement swap
dialDial conditionDial surface pristine; mystery seconds hand not touching dial surfaceMystery seconds hand touching dial; bent hand or dial deformation
Common legitimate replacements
  • Leather strap; Maurice Lacroix OEM.
  • Crystal; sapphire standard.
Expert resources: Maurice Lacroix Masterpiece Seconde Mysterieuse documentation; specialist service only for mystery mechanism.

Authentication guide

Last reviewed June 2026

The Masterpiece Seconde Mystérieuse uses the ML187 caliber; the seconds hand appears to float without a visible connection to the movement, which is the defining authentication anchor.

Known reproduction risks

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LOW

The complexity of the mystery seconds mechanism makes it a poor reproduction target; mechanical replicas of this complication are rare.

  • The seconds disc should rotate as a smooth continuous unit; a disc with a visible center pivot is not the mystery mechanism.
  • At 30m water resistance, this is a dress watch; misrepresentation is more likely to involve condition than originality.

Dial variants by era

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EraDescriptionIdentifiers
2012 to presentSilver or white dial; the mystery seconds subdial at 6 o'clock appears to rotate without a visible center arbor; Arabic numerals; 43mm case.
  • MASTERPIECE SECONDE MYSTERIEUSE on dial
  • ML187 on caseback
  • Mystery seconds subdial with apparent floating hand
  • Arabic numerals, 43mm round case

Service part flags

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Mystery seconds mechanism

Original: The seconds hand is mounted in a rotating disc driven by an off-center drive; the connection is hidden within the disc structure, giving the floating appearance.

Replacement tells
  • A conventional seconds hand with a visible center pivot is a different movement; the mystery mechanism is the entire point of this reference.
  • The seconds subdial disc should rotate smoothly as a unit; a jumping or stopping seconds display indicates mechanism damage.
Dial

Original: Clean open dial with the mystery subdial as the focal point; applied Arabic numerals.

Replacement tells
  • Printed Arabic numerals in place of applied indicate a non-original dial.

Case back markings

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2012 to present
  • MAURICE LACROIX MASTERPIECE
  • ML187 caliber designation
  • SWISS MADE
  • Display caseback showing the movement architecture

Movement tells

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  • The ML187 runs at 21,600bph; a faster beat rate suggests movement substitution.
  • The mystery seconds mechanism is integral to the movement architecture; a standard three-hand movement cannot recreate the effect.
  • The caseback view should show the unique drive wheel arrangement that powers the mystery display.
Sources: Maurice Lacroix Masterpiece Seconde Mystérieuse; Hodinkee — ML Masterpiece Seconde Mystérieuse.

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