Answer
Caliber 1861 is a hand-wound Omega chronograph movement. It has 18 jewels, beats 21,600 times per hour, and runs 48 hours on a full wind. Omega used it in the Speedmaster Professional from 1996 to 2021. Replica listings that name cal 1861 do not, in most cases, contain one. Sellers fit a Seagull ST19, a Valjoux 7750 clone, or a quartz module. Each one leaves marks a buyer can see with a loupe, a caliper, and a stopwatch.
Caliber 1861: baseline specs
- Type: hand-wound chronograph, cam switching
- Jewels: 18
- Frequency: 21,600 vph (3 Hz)
- Power reserve: 48 hours
- Diameter: 27.0 mm. Height: 6.87 mm
- Base: Lemania 1873, supplied to Omega as caliber 861 before 1996
- Hacking: no. The balance keeps running with the crown pulled
- Finish: rhodium plated. Caliber 1863 is the same design with a decorated finish for display backs
- Dial layout: 30-minute counter at 3, 12-hour counter at 6, small seconds at 9
What replica cases hold
Seagull ST19. The ST19 family comes from the Venus 175. It uses a column wheel, runs at 21,600 vph, and carries about 40 hours of reserve. Its subdials sit at 3, 6, and 9, so the dial layout matches the Moonwatch. Winding feel is lighter and the reset is softer.
Valjoux 7750 clone. Automatic, thicker, and built with subdials at 12, 6, and 9. The 30-minute counter sits at 12 instead of 3. That one detail rules out a Moonwatch dial.
Quartz. The small seconds hand at 9 o'clock jumps once per second. A sweeping chrono hand that ticks in one-second steps is a stepping motor, not a mechanical gear train.
Checks with numbers
- Case: 42 mm wide, about 48 mm lug to lug, about 14 mm thick, 20 mm lugs, 50 m water resistance. Sources differ on thickness by a few tenths. A 7750-based replica reads thicker than 15 mm.
- Caseback: reference 3570.50 is steel with a seahorse medallion. Reference 3573.50 has a sapphire display back. A display back on a Hesalite-front build is a mismatch.
- Crystal: Hesalite on 3570.50, sapphire on 3573.50. Mineral glass shows a different dome and edge tint.
- Bezel: anodized aluminum insert with a tachymeter scale. Check the dot position at 90.
- Chronograph: cam-actuated start with a firm click and a hard reset snap. The reset on a cam system has no ratchet sound.
- Dial: 1861-era Moowatches use Super-LumiNova and print SWISS MADE. Older tritium dials print T SWISS MADE T.
What a check cannot prove
A case can be copied. A dial can be copied. A serviced 1861 with a clean bridge shape and the correct engraving cannot. Photos of a movement sent by a seller are not proof of the watch on the bench. The 2021 replacement, caliber 3861, runs at 25,200 vph with a 50-hour reserve, a Co-Axial escapement, and METAS certification. That change gives buyers one more data point: a watch sold as a new 1861 Moonwatch is a watch built before 2021.