The fastest test for a fake IW371704 is the subdial layout. The IWC Portuguese Chronograph puts its chronograph minutes counter at 12 o'clock and its running seconds at 6, and any copy worth a second look has to reproduce that bicompax arrangement. A build based on an untouched Valjoux 7750 or a quartz module almost always leaves the running seconds at 9 o'clock or keeps a date window the original never had. If you want one answer and nothing else: the only tier worth considering is the one with a reworked movement and a true 12 and 6 layout. Everything below that is a costume piece. The sections below rank the checks by how much each one tells you, followed by the three quality tiers you will meet in the market.
Check 1: Subdial layout and movement
IWC based the Portuguese Chronograph on a reworked Valjoux 7750, which the company lists as calibre 79350. The stock 7750 has subdial stations at 9, 12 and 6. To reach the 12 and 6 arrangement of the original, a maker must rework the gear train, fit a custom plate, or use a dedicated chronograph clone. That work is the largest single difference between a serious copy and a cheap one, and it shows up in the cost of the movement long before it shows up in the finish of the case.
- Pros: one clear photo of the dial settles the question. Quartz builds and stock 7750 builds are exposed at the same moment.
- Cons: many listings hide the movement, and a correct layout does not by itself prove decent finishing or a working chronograph.
Use this check when the seller posts a movement photo or a short video with the chronograph running. If neither exists, ask for one before you look at anything else.
Check 2: Case, crystal and proportions
The Portuguese Chronograph is roughly 41 mm across, with a thin bezel, a domed sapphire crystal and a crown that sits close to the case band. Copies often get the diameter right and the thickness wrong, or fit a flat crystal that reflects in a hard line instead of a soft curve. Look at pusher length, lug shape, and whether the crystal carries an anti-reflective coating that keeps the dial readable from an angle.
- Pros: measurements are objective. A caliper and a bright lamp beat any opinion, and thickness is hard to fake in a listing that quotes real numbers.
- Cons: polishing and wear change the numbers on older examples, and a correct case says nothing about what sits inside it.
Use this check when you can handle the watch, or when a seller publishes measured dimensions rather than borrowed spec sheets.
Check 3: Dial furniture and printing
Look at the applied markers, the leaf-shaped hands, and the subdial rings. On a good dial the printing is thin and sharp under magnification, the markers sit level with even gaps, and the subdial rings have a fine circular texture that catches light in rings rather than patches. Common faults on fakes include markers that float above the dial, printing that thickens at the curves, hands that are too wide at the base, and luminous material where the reference calls for none at all.
- Pros: dial work is visible in ordinary photos, so you can judge it without special tools.
- Cons: photo compression hides fine printing, and harsh studio lighting flatters weak dials.
Use this check when the seller offers daylight photos of the dial at an angle, not just a straight-on hero shot.
Check 4: Caseback engraving and stamping
Reference and serial stamping is where budget copies fall apart. Original engraving is fine, even in depth, and consistent in font across every character. Fakes tend to show shallow laser marks, uneven spacing, or a font that changes weight between digits. On examples with a display back, check the rotor engraving and the movement finish through the crystal, since a decorated rotor over a plain movement is a common shortcut.
- Pros: engraving is small and hard to reproduce, so it separates tiers quickly.
- Cons: you need a close macro photo to judge it, and polishing can soften genuine stamping on older watches.
Use this check when a seller provides a macro shot of the caseback edge and the clasp, where stamping quality is usually weakest.
Check 5: Weight, strap and hardware
A steel case of this size should feel dense in the hand, and the strap should hold its shape without curling at the lugs. Thin, hollow-feeling cases and stiff, glossy straps are the usual signs of a low tier build. Check the buckle or clasp for sharp edges and shallow engraving, and check that spring bars sit tight without rattle.
- Pros: weight and feel are hard to fake and need no tools.
- Cons: feel is subjective, and a good strap can be fitted to a weak watch to raise the impression.
Use this check when you can hold the watch before committing, or when the seller shows the strap and clasp up close.
The three tiers of fake IW371704
Almost every copy on the market falls into one of three groups, and the group matters more than any single photo.
Tier 1: quartz and low-grade automatic
Wrong subdial layout, flat mineral glass, printed rather than applied markers. The chronograph may not function at all.
- Pros: the cheapest way to own the look, and fine for costume use.
- Cons: wrong dial layout, wrong crystal, weak case finish, no resale value.
Recommended only as a novelty piece you never intend to show anyone who knows the model.
Tier 2: Asian 7750 builds
Real steel cases and a working chronograph, but usually with the running seconds at 9 o'clock or a leftover date window. Case thickness often runs over spec.
- Pros: functional chronograph, solid case, decent daily wear.
- Cons: visible layout errors to anyone who knows the reference, and movements that are costly to service.
Recommended for wearers who want a mechanical chronograph and do not mind the wrong subdial axis.
Tier 3: high-grade copies with a reworked movement
True 12 and 6 layout, domed sapphire with coating, applied markers, sharp printing, and caseback stamping that survives a macro lens.
- Pros: closest visual match to the original, correct proportions and layout.
- Cons: higher cost, harder to find, and servicing still depends on a watchmaker willing to work on the movement.
Recommended for buyers who want the closest match and are prepared to pay for movement work rather than dial decoration.
What to ask a seller
- A movement photo with the caseback removed, or a video of the chronograph starting, stopping and resetting.
- Measured case diameter and thickness, taken with a caliper rather than copied from a spec sheet.
- Macro photos of the dial printing, the caseback stamping and the clasp.
- Confirmation of the subdial function at 6 o'clock: running seconds or chronograph hours.
- Whether the crystal is sapphire with anti-reflective coating on one side or both.
If a seller answers all five, you are dealing with someone who knows the model. If they answer none, the tier is almost certainly the first one.