The short answer
A fake Datograph Up/Down fails on four checks: the outsize date, the power reserve indicator, the movement finish, and the case proportions. A genuine A. Lange & Söhne Datograph Up/Down runs the in-house hand-wound calibre L951.6 with a 60 hour power reserve inside a 41 mm case. Replicas use stock chronograph base movements with decorative plates added on top. The tells therefore live in the mechanics and the calendar mechanism, not in the engraving on the caseback.
Prerequisites
- A 10x loupe
- A bright light you can angle across the dial and the movement
- The reference number of the watch and a set of clear photos of a genuine example
- Ten minutes to cycle the chronograph and let the power reserve run down
Why this watch resists copying
The Datograph Up/Down carries a column wheel chronograph with a flyback function and a precisely jumping minute counter. The movement shows Glashütte ribbing on a three-quarter plate, a hand-engraved balance cock, screwed gold chatons, and heat-blued screws. Each of those details costs hours of hand work. A counterfeit at any price point cannot fund that labor, so the fakers fake the appearance and skip the behavior.
Four checks that settle it
1. The outsize date
Set the watch close to midnight and watch the two date discs. On a genuine piece both discs jump at the same instant and land square in the aperture. On a fake the discs drag, snap at different times, or sit unevenly with one digit higher than the other. Look at the printed numerals as well. Genuine date discs have crisp, evenly inked digits with consistent stroke width.
2. The power reserve indicator
The Auf/Ab scale on the upper dial moves in a smooth, continuous arc as the mainspring winds down. Wind the watch fully, note the position of the hand, then let it run for several hours. The hand should track the real state of the mainspring. Fakes often wire the indicator to the crown or freeze it in one position, so it reads full until the movement dies.
3. The movement
Run the chronograph and watch the minute counter at the moment the sweep hand passes twelve. A real Datograph advances the minute counter in a single instant jump. A fake lets the minute hand creep forward over several seconds. Then look through the sapphire caseback at the finishing, the shape of the balance cock, and whether the engraved signature matches the pattern used in that production year.
4. Case, lugs, and dial printing
Measure the case across the bezel and check the lug profile against the reference. Fakes run thick, with soft lug edges and a bezel that is too wide. Printed text should be sharp under a loupe, with no bleeding into the dial finish. Subdial rings should be perfectly concentric with the hands.
Inspection procedure
- Ask the seller for the reference number and the year of production before you handle the watch.
- Compare the case dimensions and lug shape with published specifications for that reference.
- Set the time to 11:58 and watch both date discs through the transition.
- Wind the watch fully and record the exact position of the power reserve hand.
- Start the chronograph and watch the minute counter as the sweep hand crosses twelve.
- Stop and reset the chronograph several times to test the flyback action.
- Inspect the movement through the caseback with the loupe for ribbing, chatons, and engraving quality.
- Check the dial printing, the subdial rings, and the hand finish at 10x.
- Compare the serial and reference numbers against the paperwork and the manufacturer's records.
- Walk away if any single check fails, since one failure usually means the others will follow.
What replicas get right
Modern fakes photograph well. Case shape, dial color, and strap hardware can look convincing in a listing image, and the caseback engraving is often close enough to fool a casual glance. That is exactly why the checks above target behavior over appearance. A fake can copy a photograph. It cannot copy an instantaneous date jump or a jumping minute counter without rebuilding the movement from scratch.
If the watch fails a check
Stop the transaction and get a written opinion from a watchmaker who services German chronographs. Do not accept a partial refund or a promise to fix the issue later. Keep your photos, the listing text, and the payment record, because those are the evidence you need if you pursue the seller.