Short answer
Omega 3520 is a case reference family, not a movement number. It belongs to the Speedmaster Day-Date, which collectors call the Mark 40. Listed references include 3520.50.00, 3520.53.00 and 3520.80.00. A replica Omega 3520 is a counterfeit of that watch. We did not find a caliber 3520 in Omega's public caliber index.
What the genuine 3520 is
- Line: Omega Speedmaster Day-Date, collector name Mark 40.
- Case: stainless steel, about 39 mm across.
- Movement: automatic chronograph. Omega lists calibre 1151 for the 3520 Day-Date line, built on the ETA 7750 family platform.
- Functions: chronograph plus day and date calendar displays. Layout changes between references.
- Crystal: sapphire on most references. Confirm per reference number, since Omega changed suppliers across the run.
Omega publishes the reference and calibre data on its own site. Use the full eight-digit reference, not the four-digit family number, when you check specs.
What replica versions change
- Movement: Asian automatic chronographs, usually copies of the ETA 7750 and 7751. Parts are not interchangeable with ETA or Omega parts.
- Thickness: clone cases often run 1 mm to 2 mm thicker than the genuine case.
- Dial: font weight, text spacing and subdial ring position differ under magnification.
- Caseback: engraving depth and stamping quality differ. Serial numbers are frequently duplicated across units.
- Bracelet: end link fit and clasp stamping are the usual weak points.
- Water resistance: often untested by the seller, regardless of the number printed on the caseback.
How to check a watch in hand
- Read the caseback. The full reference and a unique serial should be engraved, not laser printed.
- Compare dial text with published photos of the same reference.
- Run the chronograph and reset it. Note the return position of the seconds hand.
- Weigh the watch head. Genuine steel cases sit in a known range for that reference.
- Ask for a movement photo with the caseback removed.
Legal status in the United States
Counterfeit watches are illegal to import and sell in the US. 18 U.S.C. 2320 sets criminal penalties for trafficking in counterfeit goods. US Customs and Border Protection seizes counterfeit shipments at the border. Trademark owners can sue sellers under the Lanham Act for damages and profits. Personal purchase carries lower exposure than resale, but goods can still be seized in transit.
Service and resale
Omega and its authorized service centers do not service counterfeits. Independent watchmakers can work on the Asian movement, but replacement parts come from the same supply channel as the watch. Resale value is near zero. Auction houses and dealers will not authenticate one as genuine.
Before you trust a spec sheet
Replica listings copy the genuine spec sheet, so the numbers on the page do not describe the watch that ships. Ask for caliper measurements, a movement photo and a caseback photo. If the seller will not provide them, the listed specs are unverified.