The short answer

A convincing fake IW371670 is judged on proportions before decoration. The genuine Portugieser Chronograph is a thin-bezel, 41 mm dress chronograph with long lugs and a wide, uncluttered dial, so a replica that gets the case profile and the subdial layout right will read as correct from arm's length even if the finishing is not perfect. A replica with a fat bezel or misplaced subdials looks wrong the moment it leaves the box, no matter how good the printing is. Ask for clear photos of the case from the side, the dial straight on, and the movement with the caseback removed. Sellers who cannot or will not provide those three shots are not worth your money.

What to look for

Case shape and dimensions

The Portugieser Chronograph sits around 41 mm across, with a slim bezel and a case height near 13 mm. The lugs are long, thin and angled, and they curve down toward the wrist instead of sticking straight out. On a good fake IW371670 the lug tips are polished, the case flanks are brushed, and the transition between the two is a crisp line rather than a soft smear. Check the crown: it should be small, fluted and sit close to the case, with two rounded pushers rather than flat discs.

Dial and subdials

Two subdials, one at 12 and one at 6, run on a vertical axis with the date window tucked at 3. The spacing matters more than anything else on the dial. Subdials that sit too close together, or a date window that crowds the subdial edge, are the fastest tells. Look at the applied numerals: thin, polished and evenly spaced, with no burrs. Printing should stay sharp under magnification, especially the minute track and the brand text. A wobbly or off-center chronograph seconds hand is a rejection.

Movement

The genuine watch runs an in-house 69000-series automatic chronograph with a column wheel and roughly 46 hours of power reserve, and it shows a smooth chronograph sweep with a clean start and stop. Replicas usually fall into three groups: a quartz or mecha-quartz module, a generic Asian automatic chronograph, or a clone of the in-house caliber. Quartz is the wrong choice here because the chronograph seconds hand ticks instead of sweeping, and anyone who knows the watch will spot that in a second. A clone movement gives you the correct look through the caseback and the right pusher feel, but it costs more and needs a service sooner.

Crystal, strap and hardware

Demand sapphire with an anti-reflective coating on both sides. Cheap mineral glass has a greenish edge and reflects like a mirror. The genuine reference ships on alligator leather with a signed pin buckle or deployant, while most replicas ship with generic leather. The strap is an easy part to replace, so treat it as a minor issue. What you should not accept is a buckle with soft engraving or a strap stitched crookedly.

Parameter bands to compare

  • Case diameter: 40.5 to 41.5 mm. Anything past 42 mm wears oversized for this design.
  • Case height: 12.5 to 13.5 mm. Under 12 mm usually means a quartz module inside.
  • Lug width: 20 mm measured between the lugs, not at the case edge.
  • Weight on leather: roughly 75 to 95 g. A hollow feeling case is a warning sign.
  • Power reserve: 40 hours or more on an automatic. Under 30 hours suggests an old or basic movement.
  • Water resistance: a 30 m rating or better. Treat higher claims as unverified unless the caseback gasket is visible in photos.

Pitfalls

  • Buying from blurry, heavily watermarked photos that crop out the case profile.
  • Assuming a higher price guarantees better quality. Cost tracks the movement and finishing only loosely.
  • Ignoring the caseback. A solid back hides shortcuts, and an open one exposes every one of them.
  • Overlooking service. A clone chronograph movement can need attention within a year of daily wear.
  • Trusting a review that never mentions subdial spacing, pusher feel or lug finishing.

FAQ

Is a fake IW371670 worth buying?

Only if you treat it as a replica and not as an investment. It is a wearable design study of a classic chronograph. Resale value is close to zero, and no seller can offer genuine parts or factory warranty service.

Which movement should I pick?

An automatic with a working chronograph and a sweeping seconds hand. That rules out plain quartz. If you want the closest visual match through an open caseback, a clone of the in-house caliber is the better option when the budget allows.

How do I spot the worst replicas fast?

Check three points: subdial spacing, the thickness of the bezel, and the finish on the lug tips. Poor examples fail at least two of them.

Can a fake IW371670 be serviced?

Yes, by an independent watchmaker, though parts availability depends on which movement is inside. Ask the seller to name the movement before you pay, and get that answer in writing.