Short answer
A fake IW371479 is a counterfeit of an IWC Portugieser Chronograph from the IW3714 family. The genuine watch measures about 40.9 mm across, uses a two-register chronograph layout with running seconds at 6 o'clock and a 30-minute counter at 12 o'clock, and on most IW3714 references the caseback is solid steel rather than glass. Copies of this model are common because a clean, uncluttered dial looks easy to reproduce. It is not. Judge the watch on four things in order: dial printing, caseback engraving, chronograph feel, and paperwork.
What the reference should show
Confirm the specification before you judge any single detail. Reference data for IW371479 controls what is correct and what is a defect.
- Case size near 40.9 mm with leaf-shaped lugs and a slim bezel
- Silver or white dial with applied faceted indices and a printed minute track
- Running seconds subdial at 6 o'clock, chronograph minutes at 12 o'clock
- Solid screw-down steel caseback on IW3714 references, with deep engraving
- Calibre 79350 base, a modified Valjoux 7750 with a 44-hour power reserve
Prerequisites
- A 10x loupe or a phone with a macro lens
- A bright, diffuse lamp and a soft lint-free cloth
- The official reference data for IW371479 open on a second screen
- A kitchen scale with 1 g resolution
- Permission from the seller to handle the watch before payment
Step-by-step checks
- Place the watch flat under the lamp and photograph the dial head-on at 10x.
- Compare the dial diameter and index spacing in your photo against the official reference image.
- Read the brand text under the loupe and check for ink bleed, uneven stroke weight, or a soft edge on the letters.
- Inspect the printed minute track for broken ticks and uneven spacing near the subdials.
- Check that each subdial hand reaches the inner track of its register without overhang or a shortfall.
- Study the applied indices for faceting and polish, since copies often use flat stamped markers.
- Look at the date aperture for a clean cut, a correct opening size, and a centered disc.
- Turn the watch over and inspect the caseback engraving depth, letter spacing, and the reference and serial format.
- Weigh the watch and compare the result against a known weight for the reference on a steel bracelet or strap.
- Push the start, stop, and reset pushers in sequence and listen for a clean, dry click with no grinding or lag.
- Pull the crown to the setting position and confirm the seconds hand hacks and the hands move without slack.
- Ask for the warranty card, booklet, and service history, then match the serial on the caseback to the paperwork.
Common tells on a fake
- Dial text that sits slightly high or low relative to the subdials
- Subdial hands that stop short of the track or sweep with visible wobble
- Caseback engraving that looks laser-etched and shallow instead of cut
- Pushers that feel spongy and reset with a snap instead of a firm click
- Case finishing with soft lug edges and a polished surface that reads too bright
- Paperwork with mismatched fonts, blank fields, or a serial that does not match the case
- A weight that is noticeably light for a steel chronograph of this size
What a visual check cannot prove
Handling and photographs catch most obvious copies, but they do not confirm the movement. A counterfeit can carry a decorated clone that looks correct through a loupe. For a high-value purchase, ask for a movement service record or have a watchmaker open the case and confirm the calibre. When the seller refuses either step, treat the price as your only signal and walk away.