Quick answer
The replica IW371717 copies the IWC Portugieser Chronograph: a stainless steel case near 40.9 mm, twin subdials at 12 and 6, a date window at 3, and an automatic chronograph movement built on the Valjoux 7750 architecture. Top-tier copies use a 7750 clone with a decorated rotor, a sapphire crystal with inner anti-reflective coating, and a dial with correct subdial spacing. Cheap versions shrink the case, print the dial with soft edges, and hide a quartz or low-grade automatic inside. The checklist below covers what to inspect before you pay.
Before you start
- Reference photos of the genuine IW371717 from a catalog scan or auction listing.
- Digital caliper, or a ruler and a steady hand.
- 10x loupe.
- Timegrapher app, or a watchmaker who can read amplitude and beat error.
- A return window confirmed in writing.
Inspection procedure
- Measure the case at the 9 and 3 o'clock points. Genuine Portugieser Chronograph references sit near 40.9 mm without the crown. A copy under 40 mm or over 42 mm has the wrong case.
- Check the lug width at 20 mm between the lugs, and confirm the strap tapers toward the buckle.
- Lay a straightedge across the crystal and the case edges. The crystal should sit near flush with a low dome. A tall, bulbous dome is a giveaway.
- Examine the crystal in daylight at 45 degrees. Look for a faint blue or purple tint from inner anti-reflective coating. Uncoated or externally coated crystals look washed out and scratch with normal wear.
- Compare subdial spacing. The 30-minute totalizer at 12 and the running seconds at 6 must sit on the vertical center line. The date aperture at 3 should be cut square and aligned with the dial print.
- Inspect the dial text under the loupe. Serif edges on the brand script and numerals should be sharp and evenly spaced. Fuzzy, double-printed, or thick text means a silk-screen shortcut.
- Check the hand finish. Leaf-shaped hands should be polished on the top facet and matte on the sides. Painted hands or half-polished hands signal a low grade.
- Wind the crown 20 turns, then start the chronograph. The pushers should click once, start from zero, and reset to exact zero without drift.
- Run the watch face up on a timegrapher for 60 seconds. Expect roughly -10 to +15 seconds per day, amplitude above 250 degrees, and beat error under 0.6 ms for a regulated 7750 base.
- Flip the caseback and read the engraving. The reference number, case material, and serial should be engraved or laser-etched into the metal, not printed on a sticker.
- Weigh the head. A steel 7750-based copy usually lands between 75 and 95 grams on the head alone. Anything near 50 grams suggests a hollow case or a quartz movement.
Movement note
The IW3717 family runs a Valjoux 7750 derivative. Copies follow two paths: an Asian 7750 clone with a decorated rotor, or a genuine ETA 7750 swap. Ask which movement is inside and request a movement photo before purchase.
Common flaws
- Subdials at 9 and 3 instead of 12 and 6, a 7753-base mistake.
- Date font that is too bold or too large.
- Caseback with the wrong reference engraving.
- Strap with machine-stitched edges where the original is hand-sewn.
Questions to ask the seller
- Which movement is inside, and can you send a photo of it?
- Are the crystal and gaskets original to this build?
- Is there a return window, and does it cover timing drift?