Quick answer
A fake IW371418 fails on measurements and details before it fails on looks. Measure the case, confirm the reference number against the official catalog, then inspect the dial text, hands, crown action, caseback engraving, and movement under magnification. Replicas of the IWC Portugieser Chronograph line get the overall silhouette close and the small text, engraving depth, and surface finishing wrong. If any single check below fails, treat the watch as not genuine until a watchmaker confirms otherwise.
What you need before you start
- A 10x loupe or a macro lens that reaches 10x.
- Digital calipers and a small scale that reads to 0.1 g.
- Reference photos of the exact IW371418 dial variant, pulled from the manufacturer's current catalog.
- A watchmaker who can remove the caseback if the watch is in hand.
Step-by-step inspection
- Measure the case diameter and thickness with calipers, then compare the numbers to the published specification for that reference. The Portugieser Chronograph case sits near 41 mm across, so a case that measures several millimeters wide of spec is not the watch you were quoted.
- Weigh the watch head and note the figure. Stainless steel cases in this line land in a narrow weight range, and a light or heavy result points to a different case material or a hollowed case.
- Look up the reference number in the official catalog and match the dial color, index style, and subdial layout to what is in front of you. Reference numbers and dial combinations are paired, and mixing them is a common replica error.
- Examine the dial printing at 10x. Check the brand name, the model line, the Swiss made marking, and the minute track. Genuine printing shows sharp edges with no bleeding into the lacquer or the metal.
- Study the hands and subdials. Look for uniform length, flat polished surfaces, and correct spacing of the small chronograph registers. Poorly cut hand edges and registers that sit off center are strong signs of a copy.
- Inspect the crystal at an angle. Genuine sapphire has an even anti reflective coating with no rainbow haze, and the coating does not wipe off with a soft cloth.
- Wind the crown and press each chronograph pusher. The crown should turn with light resistance and the pushers should snap. A gritty crown, a pusher that sticks, or a chronograph hand that jumps instead of sweeping points to a substitute movement.
- Turn the watch over and read the caseback engraving at 10x. Check the reference, the serial, the material marking, and the font weight. Genuine engraving is cut or laser marked with crisp edges, while many copies show shallow, rounded lettering.
- Compare the movement through the display back against photos of the correct caliber for that reference. Older Portugieser Chronograph models use a modified Valjoux 7750 base, so confirm the caliber first, then check rotor engraving, jewel count, and finishing.
- Check the strap or bracelet and the buckle hardware. Stitching density, leather grain, and the shape of the folding clasp should match the period-correct fittings for the reference.
- Cross check the serial number on the caseback with the papers and the warranty card. Mismatched numbers, or a serial that returns a different model in a dealer database, settles the question.
Red flags in an online listing
- Photos that avoid the caseback, the crown, or the clasp.
- A price far under the current secondary market range for the reference.
- Stock images used instead of photos of the actual watch.
- A seller who refuses a video call or a third party inspection.
- Papers that look freshly printed, with flat ink instead of embossed or foil detail.
Where high grade replicas fall short
Top tier 1:1 copies of this model often pass a glance and a wrist test. They still miss on three things: measured dimensions, engraving depth, and movement finishing. Case thickness runs slightly off because the replica case is built around a generic chronograph module, the caseback text is stamped rather than cut, and the rotor decoration does not match the real caliber layout. A watchmaker with the caseback open resolves all three in minutes.
Frequently asked
Can a serial number check prove authenticity?
No. A serial only proves the number exists on a record. It has to match the reference, the dial variant, and the caseback engraving before it means anything.
Is a service receipt enough proof?
No. Receipts are easy to fake and prove only that someone paid a bill, not that the watch is genuine.