Short Answer
A fake Jaeger-LeCoultre Reverso 3988420 usually fails in four places: the sliding carriage, the caseback engraving, the guilloche dial, and the movement finish. The carriage is the fastest test. On a genuine Reverso the case slides on its rails with even resistance, locks with a firm detent, and flips back flush with no play. Replicas bind, rattle, or leave a visible gap at the rail. If the carriage feels loose, keep going through the rest of the list before you spend money.
What You Need
- A 10x jeweler's loupe
- A digital caliper and a gram scale
- The brand's published specification for reference 3988420
- Bright, angled light
- Access to a watchmaker for a caseback opening
Step-by-Step Checks
- Pull the official specification for 3988420 and write down case size, thickness, case metal, movement caliber, and water resistance. Every check below is a comparison against those numbers.
- Measure the case with a caliper across the widest point and front to back. Replicas run large or thick because the body is built around a stock movement.
- Weigh the watch head on a gram scale. A steel or gold case carries a known mass, and a plated brass body reads light.
- Flip the carriage twenty times and count any stutter, side play, or moment where the case does not sit flush.
- Look at the rail gap with the loupe. A genuine Reverso closes with a hairline seam that runs true on both sides.
- Read the caseback engraving under the loupe. Genuine stamps have crisp edges, correct letterforms, and depth. Laser etching on fakes looks grey and shallow.
- Compare the reference number and serial number to the warranty card and box label. They should match exactly, including digit spacing.
- Study the guilloche. Lines should be cut with clean walls, spaced evenly, and centered on the dial. Fakes show wavy lines, tool marks, or a pattern that drifts off center.
- Check the printed text. The brand name, model name, and Swiss Made marking should be sharp, evenly weighted, and free of ink bleed.
- Inspect the hands at 10x. Tips should reach their markers, edges should be polished, and blued hands should show deep blue rather than paint.
- Set the second face on the Duoface. The crown should switch function with a distinct click and the 24-hour track should align with the hour hand.
- Wind the crown slowly. A genuine movement gives steady resistance and a fine ratchet. A cheap one feels sandy or spins free.
- Angle the crystal under light. Sapphire with an anti-reflective coating shows a faint blue or purple tint at one angle. Plastic or uncoated glass shows rainbow flare.
- Have a watchmaker open the case. Perlage, Geneva stripes, blued screws, jewel count, and bridge engraving are the hardest details to copy at price.
- Examine the strap, buckle, box, and papers. Stitching density, buckle finishing, box print quality, and card microprint follow the same standard as the watch.
Where Replicas Fail Most Often
Carriage tension is the first failure. Dial guilloche is the second, because the pattern needs a multi-axis cut that cheap tooling cannot hold. Movement finish is the third and the hardest to copy at low cost, which is why most replicas use a solid caseback. If a Reverso 3988420 has a display back and the decoration looks flat or painted, treat the watch as fake.
If You Are Buying
Ask for photos of the movement, the caseback engraving, and the serial on the papers before you pay. Send the watch to a watchmaker for a service quote, since a genuine Jaeger-LeCoultre movement is serviceable and a replica usually is not. A price far under market for a Reverso 3988420 with box and papers is not a bargain, it is the warning.