The short answer
A fake IW371741 is almost always a 40.9 mm Portugieser Chronograph copy, and it lives or dies on three things: the dial printing, the gap between the two subdials, and the date window. Get those right and most people will never look twice. Get them wrong and the watch reads as a replica from across a table.
The reference number trips people up. IWC's Portugieser Chronograph line runs through the 3717 family, and you will see it listed as IW371741, IW3717-41, or just 3717 depending on the seller. The checks below hold either way.
What the genuine watch gives you
The original is a steel chronograph at roughly 40.9 mm across and 12.3 mm thick, with a domed sapphire crystal, a thin bezel, and a dial that is mostly open space. Inside sits the IWC calibre 79350, a Valjoux 7750 base that IWC reworked. That matters for replicas. The 7750 architecture is easy to copy, so the movement alone rarely gives a fake away.
The dial is where the money goes. Applied numerals, a printed minute track, two subdials at 12 and 6, and a date at 3 on the versions that have one.
Dial printing and numerals
On a good copy, "IWC SCHAFFHAUSEN" sits crisp and level, with even stroke weight. I look at the gap between the letters and the outer track. Replicas tend to print slightly heavy, or the text sits a hair low. The applied numerals should have sharp inner corners and a polished bevel that catches light in one continuous line.
Subdial spacing and hand length
This is the tell I trust most. The two subdials should sit on the vertical axis with even margins, and the small hands should reach close to the minute track inside each register without touching it. Cheap copies use short hands, and the subdial rings look wide and clumsy. On A7750-based builds, subdial positions can drift a fraction of a millimeter, which shows up as a lopsided gap.
The date window
A date wheel with the wrong font is a dead giveaway. The numeral should be thin and clean, centered in the aperture, with no printing bleeding at the edges. Some fakes also cut the window too large and skip the beveled frame.
Case, crown and caseback
Case finishing separates the tiers. Look for a brushed band with polished lugs, and a lug curve that flows into the strap without a step. Engraving on the caseback should be deep and sharp, not laser faint. The crown logo is small, so check it with a loupe.
What "1:1" actually means
Nobody makes a perfect copy of a watch. "1:1" is shorthand for a build that matches dimensions, dial layout and outside finishing closely enough that the difference only shows under magnification. First-copy and super-clone language means the same thing in practice. What changes between price tiers is the dial supplier, the hand set, and how much time went into the movement.
Buying checklist
- Ask which movement is inside. A7750 is standard; a decorated clone costs more and looks closer.
- Request macro photos of the dial, especially the printing and the date window.
- Check subdial hand length against photos of a genuine example.
- Compare case thickness. Anything over about 13 mm is a red flag.
- Confirm the crystal has anti-reflective coating on both sides. The gen has a faint blue tint at angles.
- Ask about strap or bracelet fit at the lugs, since that is where cheap builds wobble.
None of this replaces seeing the watch in hand, but it filters out most of the noise before you spend anything.