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Top-tier supplier movement · caliber ETA/Valjoux 7750: Swiss automatic chronograph, 28,800bph, 42h PR, 25j; cam-and-lever system (column-wheel optional), workhorse chronograph ebauche · 42h power reserve

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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

Anti-reflective coating on both crystal surfaces must be intact; lost coating significantly reduces legibility.

Known issues in the market
  • Crystal AR coating is applied on both sides; strong reflections indicate coating loss.
  • Cal. 7750 cam-actuated architecture is correct for the 103 St Sa.
AreaWhat to checkWhat is correctRed flag
crystalDual-side AR coatingMinimal reflection from both inner and outer crystal surfaces; legibility maintained at all anglesStrong reflections from either crystal surface; coating loss visible as color shift at angles
casebackValjoux 7750 caliberETA/Valjoux 7750 architecture; Sinn serial number; 103 designation on casebackNon-7750 movement; incorrect caliber; serial inconsistent with 103 production
caseMatte pilot caseMatte brushed case surface appropriate for aviation tool watch; no polishingPolished case sections; mirror finishing inconsistent with 103 St Sa specification
Common legitimate replacements
  • Original Sinn leather pilot strap; factory replacement options through Sinn.
Expert resources: Sinn 103 St Sa product documentation at sinn.de. ETA Valjoux 7750 documentation.

Authentication guide

Last reviewed June 2026

The 103 St Sa is Sinn's classic pilot chronograph, directly descended from the original Sinn 103 design. The Valjoux 7750 movement with day/date/small-seconds and the telemeter or tachymeter bezel scale are the defining features. Low replica risk, but movement condition is the main concern on pre-owned examples.

Known reproduction risks

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LOW

Minimal replica exposure. The 103 is a niche pilot chronograph. The main risk is worn or incorrectly serviced examples with replaced dials or non-original hands.

  • Dial text or print quality inconsistent with Sinn production standards
  • Sub-dial layout inconsistent with Valjoux 7750 configuration
  • Lume color inconsistency between hands and dial

Dial variants by era

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EraDescriptionIdentifiers
2003 to presentMatte black pilot chronograph dial with all three Valjoux 7750 registers (30-min at 12, running seconds at 9, 12-hour at 6), plus a day and date display. Telemeter or tachymeter scale on the inner dial ring.
  • "SINN" and "103 St Sa" text on the dial
  • Three chronograph sub-dials at 12, 9, and 6 in Valjoux 7750 layout
  • Day and date complication: separate day display and date window
  • Small seconds sub-dial as part of the 7750 architecture
  • Telemeter or tachymeter scale around the inner dial ring
  • Matte black dial with Arabic numerals and luminous plots

Service part flags

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Day/date display

Original: The 103 St Sa has both a day-of-week display and a date window, both driven by the Valjoux 7750's day/date mechanism. Both should advance at midnight. The day should be available in multiple languages depending on the disc fitted.

Replacement tells
  • Day window text in incorrect language for the stated variant -- disc swaps are possible at service
  • Day and date that do not advance together at midnight -- they should advance simultaneously on the 7750
  • Any date display that advances gradually rather than snapping cleanly at midnight
Bezel scale

Original: The rotating bezel carries a telemeter or tachymeter scale engraved and filled. The scale is a functional pilot/aviation reference tool. Engraving should have depth and consistent fill under loupe.

Replacement tells
  • Bezel scale markings that appear printed flat without depth under loupe
  • Bezel that does not rotate -- the 103 St Sa bezel is bidirectionally rotatable for scale use
  • Scale calibration text ("TELEMETRIC" or "TACHYMETER") that is incorrect or absent
Lume on pilot hands and indices

Original: Modern production uses Super-LumiNova. Vintage or early examples may have patinated lume. The lume on the hands and indices should be consistent in color and character across all elements on the same watch.

Replacement tells
  • Mixed lume character across hands and dial (some bright new Luminova, some aged material) indicating partial replacement
  • Lume that glows a different color in darkness on hands vs. dial indices -- indicates different lume material from different production periods

Case back markings

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2003 to present
  • "SINN SPEZIALUHREN" and "GERMANY"
  • "103 St Sa" reference identification
  • "WATER RESIST 200M" depth rating
  • TEGIMENT notation on TEGIMENT variants
  • Serial number on case band

Movement tells

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  • Valjoux 7750 beats at 28,800bph. Power reserve is 42 hours. A fully wound 103 stopping before 36 hours warrants service.
  • Chronograph reset should be decisive and instant with all hands returning to zero together. Creeping or sequential reset indicates worn heart cam assembly.
  • Day change can be triggered by rapidly advancing the date through midnight using the quickset. The day should follow the date disc. If the day does not advance, the day cam is worn.
  • The 7750 is a cam-lever chronograph. The pusher feel is firm but not as crisp as a column-wheel chronograph. This is correct behavior, not a defect.
Sources: Sinn -- 103 St Sa specification and history; WatchUSeek -- Sinn pilot chronograph authentication discussion.

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