Short answer
A fake IW371770 fails on the dial first. Genuine IWC 3717-family chronographs carry crisp, evenly weighted printing, a day and a date that share one clean aperture at 3 o'clock, and pushers that snap through start, stop, and reset. Replicas usually miss two of those three. Under a loupe, the gaps are not subtle.
Know the reference before you judge the watch
IW371770 sits inside IWC's 3717 numbering block, the 42 mm chronograph family built around a 7750-based automatic caliber with a day and date calendar. Several dial and case variants share that block, so confirm the exact variant on IWC's own catalog page before you compare a watch against a photo. A silver dial measured against a black dial image will always look wrong, and that mistake pushes buyers into false panic in both directions.
What you need
- A phone camera with a 1x lens and good light
- A 10x jeweler's loupe
- A caliper or a ruler with millimeter marks
- A kitchen scale that reads grams
- A watchmaker willing to open the caseback
Step-by-step authentication
- Place the watch flat on a neutral surface and photograph the dial straight on with the 1x lens, then crop to the dial and hold it next to a catalog image of the same variant.
- Read the dial text at arm's length and check the letterforms of IWC, SCHAFFHAUSEN, and AUTOMATIC for weight, spacing, and kerning that matches the catalog.
- Inspect the day and date through the loupe and confirm both sit on the same baseline, centered in one aperture, with flat matte wheels instead of glossy printed stickers.
- Identify which subdial runs as the constant seconds hand and compare its layout to IWC's published dial for that reference.
- Start the chronograph, let it run for ten seconds, stop it, and reset it, watching for a clean snap to zero instead of a lazy drift.
- Press each pusher slowly and judge the travel, since genuine pushers move with a firm mechanical click and no gritty rasp.
- Screw the crown in and out three times and feel for smooth threads with no wobble at the stem.
- Turn the watch over and compare the caseback engraving to a known example, checking the reference number, the serial digits, and the depth of the cut.
- Measure the case across the bezel without the crown and weigh the watch, then compare both numbers to the published specs for the reference.
- Ask a watchmaker to open the caseback and photograph the movement, then compare the rotor, bridge finishing, and balance position to the caliber IWC lists for that reference.
- Check the serial against the papers, the box, and the seller's history before any money moves.
Red flags you can catch in photos alone
- Dial print that looks soft, thick, or crowded at the bottom half
- A day wheel that shows the wrong language set for the market the watch was sold in
- Subdials that sit off center or crowd the date window
- Caseback text etched shallow enough to catch a fingernail
- Pushers that sit proud of the case or thread in at an angle
- A price that lands far under the going used rate for a 3717 chronograph
What premium replicas still get wrong
High-end copies of the 3717 block have closed a lot of ground on the case and the crystal. The movement is where they stay behind. A 7750-based IWC caliber carries finishing, rotor engraving, and regulation that a generic clone does not reproduce, and a watchmaker can spot the difference in under a minute with the caseback open. Buyer beware listings sometimes show a genuine movement photo and ship a different watch, so ask for a timestamped shot.
Papers, serials, and price
Ask for the serial number before you agree to anything and cross-check it against service records or a dealer database. On a genuine watch, the serial on the caseback, the papers, and any service card should all tell the same story. Pricing is the fastest filter: a real 3717 chronograph trades at a level that no replica can match, so a bargain price is the strongest evidence you will get.
If you are shopping for a replica on purpose
Buy from a seller who states plainly that the watch is a replica. Disclosed copies are a style choice. Undisclosed ones are fraud, and the same tells listed above are what get a seller caught. Never list a replica as genuine, and never pass one on to a buyer who thinks it is real.