Short answer
A fake IW371790 is a copy of an IWC Portugieser Chronograph. Four checks settle most cases: measured case size, dial print seen under a loupe, movement finish through the display back, and the reference engraving on the caseback. A replica fails at least one of the four.
What IW371790 refers to
IW371790 is one IWC reference number. IWC uses these numbers to label a single case, dial, hand and strap combination inside a model family. The 3717 block sits in the Portugieser Chronograph line. Confirm the exact configuration with IWC or an authorized dealer before you compare a watch to a listing photo. One family holds dozens of near-identical references, so a number mismatch alone is not proof.
Portugieser Chronograph sizes: 40.9 mm for the ref 3714 generation, 41 mm for the ref 3716 generation that arrived in 2020. Both use two subdials stacked at 12 and 6 o'clock. Steel models carry 30 m water resistance.
Case measurements
Use a caliper. A 40.9 mm case reads 40.8 mm to 41.0 mm across the bezel at 3 to 9 o'clock. Replica cases run wide by 0.3 mm to 1 mm, or measure correct and sit thick, because the caseback adds 1 mm to 2 mm to clear a stock 7750 movement. Compare lug width and case thickness to IWC's published data for the reference.
Weight is a coarse filter. A steel case with a display back and a 7750 base movement carries more mass than a plated zinc case of the same size. A hand with a scale gives you a number in seconds.
Dial and hands
- Applied numerals: real ones are cut from solid metal, polished on top and grained on the sides. Copies use stamped or glued numerals with flat tops.
- Print: check the position, weight and kerning of the "IWC" and "SCHAFFHAUSEN" text against IWC photos for the reference.
- Subdials: spacing on the 3714 and 3716 sits on the vertical axis. Copies built on a different base movement shift the counters a fraction toward the center.
- Hands: feuille hands have a polished bevel and a sharp center ridge. Replica hands run thick and dull, and the chronograph needle shows tool marks.
- Minute track: hash marks on the real dial are crisp and even. Copies show bleed and uneven spacing.
Movement and caseback
Portugieser Chronograph watches have a sapphire display back. Look through it.
- Ref 3714 uses calibre 79350, based on the Valjoux 7750.
- Ref 3716 uses calibre 69355, made in Schaffhausen.
Replicas ship with a copy of the 7750. Signs: unfinished bridges, no Geneva stripes, a stamped rotor, and a chronograph seconds hand that jumps or stutters on start. The reference and serial numbers are engraved on the caseback. Compare the font and depth to IWC's own marking, not to a render.
Price signals
Replica IW371790 listings run from about $180 to $700. A seller who asks $1,500 for a replica is not selling a better watch. Genuine steel Portugieser Chronograph watches trade in the thousands on the secondary market. A claimed genuine watch under $1,000 is not genuine.
Steps before you buy
- Ask for the reference number on the caseback and match it to IWC data.
- Ask for a caliper photo of case diameter and thickness.
- Ask for a loupe photo of the dial print, numerals and subdials.
- Ask for a photo through the display back with the chronograph running.
- Ask for a photo of the caseback engraving and the buckle markings.
- Compare the asking price against the replica range and the genuine range.
What photos cannot show
Weight, hand finish, crown action and chronograph feel. A seller can photograph a real watch and ship a copy. Pay with a method that allows a chargeback, and check the return window before you send money. If the seller cannot supply the six photos above, stop.