Quick answer
A counterfeit IW371629 usually gives itself away in three places: the case, the dial, and the movement. Measure the case with calipers, read the dial text under a loupe, and put your ear and hands on the chronograph pushers. If any of those three checks fails, stop and walk away. No amount of box or paperwork fixes a wrong case or a wrong movement.
The IW371629 is a steel Portugieser Chronograph, a reference family that has been copied harder than almost any other IWC model. The copies range from cheap quartz builds to "super clone" watches with a decorated Chinese chronograph movement. Each one fails a different check, so run all of them.
Before you start
- Digital calipers that read to 0.01 mm
- A 10x jeweler's loupe or a phone macro lens
- A kitchen scale accurate to 1 gram
- The official spec sheet for the exact IW371629 variant you are looking at
- Bright, raking light and a clean dark cloth
Authentication walkthrough
- Pull the official reference page for the exact IW371629 variant and write down the case diameter, case thickness, lug width, dial finish, and movement calibre. Every later step gets compared against this list.
- Measure the case across the 9 to 3 line with calipers, crown and pushers excluded. Genuine Portugieser Chronograph cases sit at 41 mm, and most copies land between 40.2 and 42.5 mm because they reuse a generic case.
- Measure the case thickness from the caseback to the top of the crystal. A copy built on a generic chronograph base is often 1 to 2 mm thicker than the real watch.
- Weigh the watch head on the scale and compare it to the published weight for the strap or bracelet variant. Counterfeit steel cases are frequently thinner-walled and lighter than they should be.
- Count the subdials and note their positions. The genuine dial runs a 30-minute counter and a running seconds hand, and the layout must match the reference you are checking, not a generic three-register chronograph layout.
- Study the dial printing under the loupe. Look for crisp edges on every letter, even weight in the strokes, and correct spacing between the brand name and the model text. Fuzzy, thick, or crowded printing is the single most common flaw on fakes.
- Inspect the applied numerals and indices for flatness and finish. Real parts are polished on the top face with sharp, straight sides and sit level on the dial.
- Check hand alignment and finish. The hands should be the correct shape for the reference, evenly polished, and set so they do not touch each other at any position.
- Press the top pusher to start the chronograph. The action should feel firm with a short, clean travel, and the central seconds hand should jump into motion without stutter.
- Press the bottom pusher to reset. The hands should snap back to zero in one motion. Sluggish or grinding reset points to a cheap module movement.
- Turn the watch over and inspect the caseback engraving under the loupe. Reference number, serial number, and material markings must be cut or laser-etched with uniform depth, straight baselines, and correct fonts.
- Examine the movement finish through the display back. Look for even striping, clean bevels on the bridges, blued or polished screws seated flush, and an engraved rotor plate. Printed or stick-on decoration over a bare movement is a fake.
- Rotate the rotor and listen. A genuine automatic winding system is nearly silent. A rattling or scraping sound suggests a low-grade rotor bearing.
- Check the crown action. Winding, date setting if applicable, and hand setting should each feel distinct, with no wobble in the stem.
- Compare the box, booklet, and warranty card against the reference date. Cards are the easiest item to counterfeit, so treat paperwork as supporting evidence only, never as proof.
- Photograph the dial, caseback, movement, and serial number, then send the images to an IWC boutique or an independent watchmaker who services the brand. A written opinion is worth more than any seller claim.
Red flags that end the deal
- A seller who refuses macro photos of the dial and movement
- A price far below the going rate for the reference
- Serial numbers that do not match between the caseback and the paperwork
- A caseback with shallow, uneven, or partly missing engraving
- Chronograph pushers that feel mushy or bind on reset
- Photos copied from another listing, which you can confirm with a reverse image search
When to get expert help
If the watch passes every check but the seller is pushing for a fast sale, pay for a professional inspection before money changes hands. A watchmaker with the caseback open can confirm the movement family in minutes, and that confirmation is the only step that cannot be faked with good photography. Budget for the inspection as part of the purchase price and treat a refusal as a no.