The short version: verify the genuine reference before you judge any fake IW371747. Get the real case diameter, thickness, lug width, dial layout, and movement family from the brand, then treat every listing as unverified until it matches those numbers. A build that measures correctly and keeps the dial architecture intact beats one with shinier finishing on a case that is two millimeters off. If a seller cannot state the movement inside, the measured case size, and the strap width, that silence is the answer.
What the reference number does and does not tell you
IW371747 belongs to IWC's chronograph family, and the number identifies one configuration inside a line that shares a case architecture while varying dial color, hands, and bracelet. Because the family is wide, many listings borrow the number and ship a case built for a different variant. The number in a listing title is a label. The measurements and the dial layout are the product.
What to look for, in order of importance
- Dial layout. Count the subdials, note their position, and confirm each one works. Decorative subdials tied to a quartz board are the most common shortcut.
- Case measurements. Ask for caliper photos: diameter across the bezel, thickness including crystal, and lug width. Published photos distort proportions.
- Hand set. Length relative to the markers, shape at the tip, and finish. Painted hands with a flat sheen sit a step below faceted, polished ones.
- Dial printing and markers. Font weight, spacing between the logo and the markers, and whether applied indices sit level on the dial.
- Movement. Ask for the caliber name, beat rate, power reserve, and whether the chronograph uses a modular add-on or a purpose-built chronograph base.
- Crown and pushers. Screw-down crown threads, pusher travel, and whether the pushers sit flush with the case band.
- Caseback. Engraving depth, reference placement, and whether the text matches the case it is screwed onto.
- Crystal. Domed or flat, and whether the anti-reflective coating is on the inside. Coating on the outside scratches and is an easy tell.
Parameter bands worth holding to
- Case diameter: 40 to 41 mm. Anything outside that range is a different variant, not this reference.
- Case thickness: roughly 12.5 to 14 mm depending on the movement fitted.
- Lug width: 20 to 21 mm, which sets the strap or bracelet choice.
- Movement: automatic chronograph at 28,800 vibrations per hour, with 40 to 60 hours of reserve. A quartz build in this case shape is a downgrade, not a bargain.
- Weight: a bare head in the 70 to 110 g range, lighter with a quartz board and heavier with a full automatic chronograph.
- Water resistance: treat 3 to 6 ATM as the realistic ceiling unless the seller pressure-tested the watch and can say so.
Pitfalls that cost the most
- Reused photos. If the same image appears across several sellers, you are looking at a stock photo, not the watch you will receive.
- Reference numbers treated as a marketing word. The number should match the case, dial, and movement together, not just the listing title.
- Quartz movements sold as automatic. Ask for a movement photo and a check of the seconds-hand sweep.
- Water resistance claims with no gasket service. A rating engraved on a caseback means nothing after the case has been opened.
- Swiss markings on an Asian movement. The engraving is cosmetic and often applied after assembly.
- Size claims without measurements. A listing that says 41 mm but never shows calipers is guessing.
FAQ
How hard is a fake IW371747 to spot in person?
From across a table, hard. In hand, the dial layout and the case thickness give it away fastest, followed by the hand finish and the pusher feel. Photos hide all three, so ask for measured shots and a short video of the chronograph running.
Which movement should I expect at this level?
An automatic chronograph, normally a chronograph-module design or a Chinese-made integrated chronograph. What matters is that the seller names it and that the subdial functions match the dial layout. An unnamed movement is the biggest single risk in this purchase.
Is a Swiss movement worth the extra cost?
Only if the case, dial, and hands are already correct. A good movement inside a wrong case still produces a watch that looks wrong on the wrist. Fix the visible parts first, then pay for the movement.
What should I check when the watch arrives?
Measure the case with calipers, run the chronograph start, stop, and reset, confirm that the subdials return to zero, wind it fully and time it over 24 hours, and inspect the crystal coating with a light at a low angle.
What matters least?
The box, the papers, and the packaging. They are cheap to reproduce and tell you nothing about the watch itself. Spend your attention on measurements and the dial.