Short answer

Judge a replica IW371650 on four points: case proportions, dial print and subdial placement, movement behavior, and the finish on the crown, pushers, and clasp. A strong example gets all four close to the genuine Portuguese Chronograph. A weak one fails on at least two, and the failure shows up in photos before you pay.

Know the real watch first

The IW371650 belongs to the IWC Portuguese Chronograph line. The modern reference uses a 41 mm stainless steel case about 13.1 mm thick, a convex sapphire crystal, a 20 mm lug width, and IWC calibre 69355 with a 46 hour power reserve. The dial carries two subdials, chronograph minutes at 12 and running seconds at 6, plus printed Arabic numerals and a railway minute track. Confirm the dial color and hand finish for IW371650 on IWC's product page before you compare, because IWC has shipped several dial variants under one case code.

How to check a replica IW371650

  1. Ask the seller for the case diameter. Genuine is 41 mm. Measure yours with calipers when it lands; a reading past 41.5 mm means a different case was used.
  2. Ask for the thickness. A replica built on a thin quartz movement comes in at 9 to 10 mm and sits flat on the wrist instead of standing tall like the real watch.
  3. Confirm the lug width at 20 mm. A correct strap should fit flush with no gap at the lugs.
  4. Look at subdial placement. Chronograph minutes at 12, running seconds at 6. A seconds hand at 9 o'clock signals a Valjoux style layout, not this reference.
  5. Run the chronograph through start, stop, and reset. The counter at 12 must advance once per full turn of the central hand. Watch whether the reset snaps to zero in one motion or drifts.
  6. Inspect the dial print under a loupe. Arabic numerals thin and upright, railway track unbroken, even spacing between the brand name and the city line, no fuzzy edges.
  7. Work the crown and pushers. Light pressure, clean return to position, no wobble. Gritty pushers are the most common tell on this model.
  8. Read the caseback engraving with a magnifier. Reference number, serial, and Swiss Made markings should be crisp, straight, and even in depth.
  9. Check the case finishing. Brushed flanks, polished bezel, sharp transition at the lug edges. Rounded or soft edges mean a cheap polish job.

Red flags

  • Stock photos instead of images of the actual watch
  • No photo of the movement through the caseback
  • Thickness under 12 mm on a claimed automatic
  • Subdials at 9 and 3 instead of 12 and 6
  • A price far below the going rate for the tier you are buying

Questions to send the seller

Ask for the movement name and beat rate, the measured thickness, the lug width, and a short video of the chronograph running. Request the serial on the caseback and a photo of the same number if the movement is visible. Sellers who answer with numbers and clips are the ones worth your money. Sellers who answer with adjectives are not.

When it arrives

  1. Measure the case with digital calipers and compare against 41 mm.
  2. Time the chronograph over 24 hours for drift.
  3. Let it run down overnight to test the stated power reserve.
  4. Do not test water resistance unless the seller states a rating, and treat any rating as a claim rather than a guarantee.

A replica IW371650 will never match a genuine Portuguese Chronograph in movement architecture or long term service support. The goal here is a watch that reads correctly on the wrist and runs without drama. Check the numbers, not the marketing copy.