Buy the version that gets the dial architecture and the case proportions right, not the cheapest one on the page. On the IW371651, and on every Portugieser Chronograph in the IW3716 family, the two counters sit on a vertical axis at 12 and 6 and they are cut into the dial rather than printed on top of it. The case is about 13 mm thick. If a replica shows flat, silkscreened subdials, or stands noticeably taller than 14 mm on the wrist, nothing else it does well will rescue the watch. Those three points decide whether the piece reads as a Portugieser from arm's length. Everything else, from the strap to the hand polish, is a detail you can fix or upgrade later.

What the IW371651 actually is

The reference belongs to the modern Portugieser Chronograph line: a 41 mm steel case, a thin bezel, a dial with a railway minute track and applied numerals, leaf-shaped (feuille) hands, a 30-minute chrono counter at 12 and running seconds at 6. There is no date, no tachymeter scale and no small seconds at 9. The movement is the in-house calibre 69355, an integrated chronograph with a column wheel, running at 28,800 vph with roughly 46 hours of reserve, visible through a sapphire caseback. Keep that spec sheet in your head, because most replica failures on this model are failures against that list, not against some vague idea of quality.

What to check before you commit

• Subdial depth. Tilt the watch under a lamp. The counters should sit below the dial surface with a visible step at the edge. Painted circles with printed snailing are the single most common shortcut.
• Subdial spacing. The gap between the 12 counter and the 6 counter should feel tight. Wide spacing usually means the maker reused a stock three-register layout and moved the hands.
• Hand shape. Leaf hands, tapered to a point at both ends, not batons and not dauphine. Look at the tip profile in macro shots.
• Case thickness. Ask for a caliper photo. This is the number sellers most often round down.
• Dial printing. The minute track and the text should be crisp under 10x. Fuzzy edges mean pad printing with worn plates.
• Crystal. Box-domed sapphire with anti-reflective coating on both faces. A strong blue tint means single-sided coating or a coated mineral glass.
• Caseback. Sapphire display, correct engraving depth, and a rotor that at least gestures at the 69355 layout rather than a generic decorated blank.

Parameter bands worth measuring

• Case diameter: 40.8 to 41.3 mm. Anything at 42 mm or above is a different case.
• Case height: 13.0 to 13.9 mm is acceptable. Above 14.2 mm the watch will sit high and the profile will look wrong.
• Lug width: 20 mm, with curved ends that follow the case flank.
• Lug to lug: roughly 47 mm. This drives how the watch wears more than the diameter does.
• Weight on a leather strap: around 70 to 85 g. A very light piece suggests a thin case shell and a hollow feel.
• Chrono counter at 12: 30 minutes per revolution, not 60. Check that the hand advances one step per minute and not two.

Which movement you are buying

Two paths exist. The cheaper one uses a Valjoux 7750 base modified to bi-compax, which is reliable and easy to service but tends to add height and produces a rotor wobble you can feel when the watch moves. The better path uses a clone of the 69355 architecture, which brings the case closer to 13 mm, gives a smoother pusher feel and puts the decoration where the caseback shows it. Neither is a bad choice, but they are different products and should be priced and judged differently. Ask which one you are getting, and ask whether the chrono hand resets cleanly to zero without a nudge. Test the pushers: firm start, crisp stop, snap-back on reset, no sponginess.

Pitfalls that give a replica away

A date window at 3 is the classic error on this model, so check the dial photo carefully. A tachymeter ring around the outer edge is another, since the Portugieser does not carry one. Look at the spacing between the 6 o'clock counter and the text above it, which should leave a clean breathing gap. On the case side, sharp lug edges and a crown that sits proud of the case flank are common. On the dial, indices that are glued rather than set into the surface and hands with visible machining marks along the bevel will show up in daylight long before anyone reads the brand text. Also watch for overly blue anti-reflective coating, which photographs well and looks wrong indoors.

FAQ

Is the 12/6 layout difficult to replicate well?

No, but it is easy to fake badly. The genuine layout is tight and recessed, and a maker who skips the recessed counters is saving real money on the dial. Judge that before anything else.

How do I verify thickness without a caliper?

Ask the seller for a photo of the watch on a flat surface next to a rule, taken square to the camera. A side profile shot against a known coin or card also works. If neither is available, assume the higher figure.

Should I pay more for the cloned movement?

Yes, if you care about the wrist profile and the caseback view. If you plan to wear it hard and want cheap servicing, the modified 7750 route is defensible, but accept the extra height.

What about the strap and clasp?

Assume both are placeholders. Budget for a decent leather strap with curved ends, since the case is designed around one, and treat the clasp as a consumable.

Will the chrono work as a daily function?

It will, but run it sparingly. Leave the chrono stopped in the normal position, avoid resetting while the hand is running, and keep the pushers dry. That routine adds years to any chronograph, replica or otherwise.