If you are shopping for a fake IW371618, the decision that matters most is the movement inside the case, not the photos on the listing. The IWC Portugieser Chronograph runs a 12 and 6 subdial layout, and that layout forces every copy to make a choice: a cheap transfer-plate module stacked on a generic chronograph, or a properly built movement with the subdials where they belong. Buyers who start with the movement and then verify case thickness, dial printing and crystal clarity end up with something that holds up on the wrist. Buyers who start with a glossy product shot end up with a watch that is two millimeters too thick and has the date sitting in the wrong spot.
What the Reference Actually Is
The IW371618 sits in the Portugieser Chronograph family: a 41 mm stainless steel case, roughly 13 mm thick, 20 mm lugs, sapphire crystal front and back, 30 m water resistance, and IWC's in-house 69355 caliber with a column wheel and vertical clutch. Knowing those real numbers gives you a checklist. A copy that misses the diameter by more than a fraction of a millimeter, or the thickness by more than half a millimeter, will sit differently on the wrist and will be obvious to anyone who has handled the genuine watch.
What to Look For
Case and thickness
Thickness is the tell. A standard three-register chronograph module adds height, so many low-tier copies come in at 14.5 mm or more. Ask for a measured side profile photo with calipers or a ruler against the caseback, not just an angled wrist shot. Check too that the lug profile curves rather than drops straight down, and that the bezel is polished while the mid-case is brushed. On the real piece that contrast is clean and deliberate.
Dial and hands
Look for applied numerals with sharp edges, subdial rings that are recessed rather than printed flat, and a date window that is centered under its aperture with the correct font. Hands should be polished and faceted, not stamped flat, and the seconds hand on the running subdial should sweep rather than tick. Printing on the dial should be crisp at macro distance; blurry or thick lettering shows up immediately under a phone camera.
Movement and chronograph action
Start the chronograph and watch the sweep. A column wheel and vertical clutch feel smooth and start without a visible jump of the seconds hand. Pushers should have short, firm travel with no mush. If the seller cannot describe the movement base or refuses a movement photo through the caseback, treat that as your answer.
Crystal, caseback and finishing
Anti-reflective coating should be applied to the inside of the crystal. An outside coating scratches and looks cloudy within months. Caseback engraving should be deep, even and legible, and the crystal caseback should show a movement that is finished rather than a plain grey plate.
Parameter Bands to Check Before You Order
- Case diameter: 40.8 to 41.2 mm
- Case thickness: 12.8 to 13.6 mm for a convincing profile
- Lug width: 20 mm, so standard straps fit
- Subdial positions: 12 o'clock and 6 o'clock, symmetric about the center
- Water resistance: claimed 30 m; never trust a copy beyond splashes
- Power reserve: 40 hours or more on the better movements
Pitfalls to Avoid
- Listings that use official brand photography instead of photos of the actual unit
- No movement shot, no caseback shot, no measurement shot
- Sellers who call every tier a "super clone" with no detail on the movement base
- Subdials at 9 and 3, which is the wrong layout for this reference
- A date window with square corners or the wrong typeface
- Skipping the strap question: cheap alligator-grain leather is a giveaway on an otherwise decent build
FAQ
Is a fake IW371618 worth buying?
Only the top tier is. Below that, the thickness and dial flaws make it read as a costume piece rather than a watch. If the budget does not reach a build with a proper movement, waiting is the better call.
How can I tell a good copy from a bad one without handling it?
Ask for four photos: a straight-on dial shot, a side profile with a ruler, a caseback shot, and a movement shot with the chronograph running. Sellers who can provide all four are working with a watch they understand.
Which movement should I expect?
The best copies use a chronograph movement with the correct 12 and 6 subdial geometry and a column wheel. Mid-tier builds use a modified generic chronograph, which works but adds height and can feel vague at the pushers.
Does the strap matter as much as the watch?
It matters more than most buyers expect. A soft, correctly stitched leather strap changes how the whole watch reads on the wrist, and it is the cheapest upgrade you can make after purchase.