Short answer
A replica IW371780 is a copy of the IWC Portugieser Chronograph. The genuine watch is a steel chronograph, 40.9 mm wide, with two subdials and a date at 3 o'clock. Copies sell from about $90 for quartz versions to about $600 for automatic versions built on a 7750 base movement. No copy uses an IWC calibre. Case thickness and subdial spacing are the two fastest tells.
IWC reference numbers in this family appear as IW3717xx. IWC does not publish a public spec sheet for every suffix. Confirm the exact reference with IWC before you compare a listing to a catalog entry.
Genuine specs to compare against
- Case diameter: 40.9 mm
- Case thickness: 12.3 mm to 13.1 mm, depending on the movement version
- Movement: calibre 79350, a modified Valjoux 7750, on earlier references; calibre 69355 on references from 2020
- Power reserve: 44 hours on 79350 versions; IWC lists 46 hours for calibre 69355
- Subdials: 30-minute counter at 12 o'clock, small seconds at 6 o'clock
- Date: window at 3 o'clock, no day wheel
- Crystal: sapphire, antireflective coating on both faces
- Caseback: sapphire display
- Water resistance: 3 bar, or 30 m
- Lug width: 20 mm; strap is alligator leather
Where copies differ
Thickness. A 7750 base movement adds height. Many automatic copies measure 14 mm to 15 mm against the genuine 12.3 mm. A caliper check on the caseback edge settles it.
Subdial spacing. The two subdials sit on a vertical line through the center. Copies that reuse a stock 7750 dial layout push the counters off center or crowd the date window.
Small seconds at 6. A 7750 runs its small seconds at 9 o'clock. Moving that hand to 6 needs a gear module. That module is the most common failure point on automatic copies. Ask the seller which movement is inside and how the seconds hand is driven.
Printing and hands. Genuine dials carry thin, sharp Arabic numerals and a fine minutes track. Copies show thicker numerals, uneven lume fill, and flat blued hands instead of heat-treated steel.
Caseback. The sapphire display should show a decorated movement with Geneva stripes and an engraved rotor. Copy engraving is shallow, and the reference string is cut with a laser, not stamped.
Checks before you pay
- Ask for the measured case thickness with a photo of calipers on the case.
- Ask for the movement name and a photo of the rotor through the caseback.
- Check the date font. Genuine numerals are narrow and sit high in the window.
- Confirm the strap width at the lugs: 20 mm, not 22 mm.
- Confirm the return terms in writing.
Legal note
Sale and import of counterfeit watches is illegal in the US. CBP can seize shipments, and 19 U.S.C. § 1526 covers trademarked goods. Treat any replica listing as a risk purchase.