The short answer
The replica worth buying is the one carrying a mechanical 7750-type chronograph with running seconds at 6 o'clock and the combined chronograph counter at 12. That register layout is the point of the model, and it is the first thing a fake gets wrong. This guide weighs four criteria: dial layout and printing, chronograph function and pusher feel, case and crystal finishing, and strap and hardware. Each section closes with a plain recommendation about who that level of build suits.
What the IW371740 is before you compare it
The reference sits inside IWC's Portuguese Chronograph line, a family with a wide near-flat bezel, long lugs that curve toward the wrist, a slim profile for a chronograph, and a dial built around two registers instead of three. Applied Arabic numerals, leaf-shaped hands, and a date window at 3 o'clock appear across most of the line. Because the design is spare, errors show: a numeral that is too thick, a date font that is wrong, or a subdial a millimeter off center is visible across a dinner table.
Handle a genuine example at a dealer or a watch show if you can. Listing photos hide exactly the details you need to judge.
Criterion 1: Dial layout and printing
Pros:
- Running seconds at 6 and the combined counter at 12, so the dial reads as a true two-register arrangement.
- Applied numerals with a polished bevel that catches light along one edge and casts a hairline shadow.
- A cleanly cut date window and a date wheel whose font matches the rest of the dial.
Cons:
- Budget builds fit three subdials, or leave the top register as a 30-minute counter only, which is the wrong function.
- Glued or pad-printed numerals sit flat and reflect nothing.
- Wrong date wheels, or a white disc behind a silver dial, break the look at a glance.
Best for: buyers who wear the watch with short sleeves and expect the dial to hold up from conversational distance.
Criterion 2: Chronograph function and pusher feel
Pros:
- A 7750-based movement gives a crisp start, a firm stop, and a single clean snap on reset.
- 28,800 vph beats produce a smoother sweep and a chronograph seconds hand that advances in small steps.
- Quickset date and a running seconds hand that keeps time without stutter.
Cons:
- A quartz chronograph hides inside the case, so the pushers feel dead and the chronograph hand jumps once per second.
- Cheap mechanicals lose amplitude, stutter, and stall when the counter passes the 12-hour mark.
- A reset that needs a second push, or grinds, points to a worn or badly assembled lever.
Best for: anyone who actually times things and wants the pusher feedback of a cam-actuated mechanical chronograph.
Criterion 3: Case, crystal, and caseback
Pros:
- Case proportions that keep the bezel thin and the lugs curving down rather than sitting flat.
- Sapphire with an anti-reflective treatment that cuts glare instead of tinting the dial blue.
- Caseback engraving deep enough to catch a fingernail, with a reference number in the correct font.
Cons:
- Over-polished cases with rounded lug edges and soft transitions between brushed and polished surfaces.
- Coatings that flash purple or blue under a shop lamp.
- Laser-etched casebacks that look frosted, or reference numbers that do not match the dial variant.
Best for: buyers who handle the watch up close, wear it under a cuff, and care about side-profile proportions.
Criterion 4: Strap, buckle, and hardware
Pros:
- Alligator-grain leather with tight, even stitching and a taper that matches the lug width.
- A buckle with crisp engraving and a tang thick enough not to flex under thumb pressure.
- Spring bars that seat without rattle in the lug holes.
Cons:
- Glossy embossed leather that creases white within days.
- Soft engraving and thin metal that bends when the strap is pulled.
- Hardware that scratches through its finish in a week of daily wear.
Best for: anyone who keeps the original strap on and judges the watch from the wrist outward.
A five-minute check before you pay
- Ask for a photo of the caseback with the reference number legible, then compare the font to the dial variant.
- Start the chronograph and let it run ten minutes. Watch whether the seconds hand steps smoothly or jumps.
- Push reset and listen for one clean snap rather than a double click.
- Set the date and watch it flip near midnight instead of drifting past it.
- Turn the watch under a lamp and view the dial at a low angle for flat print or a milky crystal.
- Slide a fingernail across the caseback text to judge how deep the engraving goes.
A replica that passes all six checks is a wearer's watch. One that fails two or more is a photograph, and photographs do not survive a handshake.