Which movements are being compared?

The names used on this page
Name Scope
ETA 2892A2 / 2892-A2 The specific ETA reference in its current manufacturer record.
Sea-Gull TY2661/ST1812 The specific automatic time-and-date movement in Sea-Gull's current product listing.
ST18 A broader label that needs a complete reference before specifications or parts can be assigned.

The comparison uses published records checked on 14 October 2026. It does not report side-by-side sample testing or establish that a replica listing contains either of these movements. A movement described only as “ST18” remains incompletely identified.

Mechanical movement close-up.
Movement photograph for the comparison.
The photograph alone does not establish a movement’s exact calibre or origin.

Published specifications and measurement limits

ETA and Sea-Gull manufacturer listings, checked 14 October 2026
Characteristic ETA 2892A2 Sea-Gull TY2661/ST1812
Diameter as described 25.60 mm Approx. 26.20 mm maximum diameter; a different stated measurement basis
Movement height 3.60 mm Approx. 3.91 mm
Jewels 21 24
Frequency entry 28,800 vibrations/hour; 4 Hz 28800; the product field does not spell out the unit
Reserve in the listing Typical 50 hours 42 hours
Display and setting features Three central hands, date and stop-seconds Three central hands, date at 3 o'clock and stop-seconds

The 2019 ETA 2892A2 technical communication instead gives 42 hours. When comparing an older ETA example, use its applicable documentation rather than automatically treating the current 50-hour listing as its specification. The 2892 family reference explains the dated records.

What the differences mean for a decision

From a published difference to a practical conclusion
Difference Useful conclusion Decision that still needs evidence
3.60 mm versus approximately 3.91 mm height The ETA entry is about 0.31 mm lower, relevant where movement space is tight. The thickness of the assembled watch and clearance for its hands or caseback.
Diameter versus maximum-diameter wording Obtain matched case-fitting dimensions before selecting a holder or replacement. Whether either movement will sit securely in the existing case.
21 versus 24 jewels The bearing arrangements need their own parts documentation. A ranking for daily accuracy, durability or service life.
Current 50-hour typical reserve versus a 42-hour listing The current ETA specification offers a larger stated running-time allowance. Which actual watch runs longer after an equivalent documented wind.

For a new watch with limited movement space, the ETA height is the relevant published advantage. For routine ownership, an identified movement with accessible service and documented behaviour is more useful than a higher jewel count. For a replacement project, the dimensions above are only the starting point.

Can an ST1812 replace a 2892A2?

The records used here are insufficient to confirm a direct replacement. Give the watchmaker both full references and the case configuration. These five matches decide whether a proposed conversion is feasible:

Replacement assessment to complete before buying parts
Required match Question for the repairer Result or drawing reference
Stem height Does the winding stem align with the existing crown tube? —
Hand-fitting dimensions Will the existing hands fit and clear the dial and crystal? —
Dial attachment Are the dial feet and their fixing arrangement compatible? —
Calendar alignment Does the date display align with the dial aperture? —
Holder and case clearance Can the movement be secured with adequate rotor and caseback clearance? —

A similar exterior does not answer these fitting questions. A proposed change that requires a new dial, hands or holder also changes the repair's cost and scope. The result cells above are intentionally unfilled.

Record the actual watch before choosing

Copyable evidence record; no sample results are supplied
Item Details to record Your result
Identity Actual maker, full reference and identification evidence —
Rate Observation dates, duration, winding state, worn/resting positions and measured difference —
Timing-machine report Unit identity, position, rate, beat error, amplitude and lift-angle setting —
Reserve Winding procedure, start time and stop time —
Service plan Repairer's acceptance, parts availability, work included and quote —

Only compare rate or reserve results taken under stated, reasonably comparable conditions. Without those results, the fair conclusion is a dimensional and specification comparison with an unresolved performance ranking. Use the quality checklist for the separate case, bracelet and support decisions.