The short answer

A fake IW371762 is a replica of an IWC Portugieser Chronograph, a slim twin register dress chronograph and one of the most frequently copied IWC shapes. The deciding evidence is the caseback and the movement, not the dial. Dials, straps and buckles get swapped between genuine and replica watches all the time, so a clean dial proves very little. If a seller will not show you the movement, the caseback engraving, or the reference and case numbers, judge the watch as a replica and price it that way.

Before any of that, pull the exact reference from the manufacturer's own catalogue and note the case size, lug width, movement type and whether the model has a display back. IW371762 sits in a large reference family with several near identical dial variants, and most mistakes come from comparing against the wrong sibling reference rather than from clever counterfeiting.

Reference and case numbers

IWC watches carry a reference number and a separate case number, and the two must appear consistently across the caseback, the paperwork and the movement. On many IWC models the reference is engraved between the lugs, which is why sellers photograph the watch lying flat but never shot from below. Laser engraving on a replica tends to look shallow, slightly grey and perfectly uniform, while a struck or deeply engraved number has visible depth under angled light.

• Pros: fast, needs no tools, and catches the majority of low grade listings in under a minute.
• Cons: a genuine caseback can be fitted to a fake case, and a re-engraved case fools this check completely.

Case and proportions

The Portugieser Chronograph is admired for a thin bezel, a wide dial opening and a case that sits low on the wrist. Replica cases usually fail on thickness and on the rehaut, the metal ring between the crystal and the dial. A thick rehaut is a sign that a small movement was dropped into a large case, which is the standard shortcut in budget replicas. Measure the case with calipers rather than trusting the listing, and check whether the lugs curve the way the reference does.

• Pros: objective and repeatable, since calipers do not care about photography or lighting.
• Cons: some genuine references changed dimensions mid production, so compare only against the correct generation.

Dial, printing and subdials

Look at the printing under magnification. Genuine dial text has crisp edges and consistent ink density, while replica printing often shows a soft halo, uneven spacing between letters, or a slightly different font weight on the subdial rings. Check the subdial spacing against the reference, then check the date window if the model has one: a window that sits too close to a subdial is a layout error, not a wear issue.

• Pros: works from good photographs, which matters when the watch is overseas.
• Cons: dials are the easiest part to replace, and high grade replicas print very well.

Movement and caseback

This is where the question is usually settled. A display back shows the movement finish, the rotor engraving, the shape of the bridges and the colour of the screws. Replica movements often use painted blue screws instead of heat blued steel, shallow or missing engraving, and a rotor that is decorated on the visible side only. Ask for a short video of the movement running, not a still photo, and ask for the chronograph to be started, stopped and reset on camera.

• Pros: hardest evidence to fake and hardest evidence to hide.
• Cons: requires a seller willing to open or film the watch, and some references have solid casebacks, which removes this option entirely.

Strap, buckle and packaging

Strap stitching, the taper of the leather, the hardness of the buckle tongue and the finish inside the clasp all separate a careful build from a rushed one. Packaging is the weakest signal of all. Boxes and cards are produced in volume and are routinely paired with replica watches to raise the price, so treat a full set as a presentation detail rather than proof.

Who this matters for

If you are buying the look, run the caseback, movement and caliper checks, because those three decide whether you are paying for a well made replica or a badly built one that will not survive a service. If you are paying genuine market money, insist on a movement inspection and a written return window, and budget for an independent watchmaker to open the watch the day it arrives. On any reference with a display back, a seller who refuses that inspection has already answered the question for you.