The fastest way to sort a watch listed as a fake Zeitwerk 306.104 from a real one is to watch the numerals change. On an A. Lange & Sohne Zeitwerk, the hour and minute discs snap to the next digit in a single instant, driven by a constant-force mechanism built for exactly that job. On a replica, the same display is usually pushed by an ordinary gear train, so the digits creep, hesitate, or land slightly off center. The reference number in the listing is a separate question: it is a claim to check against the maker's own records, never proof by itself. What follows is the order worth using, from the mechanism outward.

Why "306.104" settles nothing on its own

Reference numbers circulate through the secondary market with typos, translation errors, and copy-paste from unrelated listings. A number that does not appear in the manufacturer's published reference list tells you the listing was assembled carelessly, and careless listings are where bad watches live. A number that does appear proves nothing either, because dials, cases, movements, and papers get swapped independently. The number is an address, not a fingerprint. Confirm it, then move on to the object.

Criterion 1: the numeral jump

Lange's digital display is not two rotating discs on a normal train. A remontoir stores energy through the minute and releases it in one motion, which is why the jump is instant and why the display stays honest across the full running time. Replica builders rarely reproduce that, because the mechanism costs more than the rest of the watch combined.

  • Watch the minute change for ten minutes or more. A real one snaps once, cleanly, at the top of each minute.
  • Check the digits inside the aperture frames. Originals sit centered and square. Replicas sit high, low, or tilted.
  • Watch the hour change at the top of the hour. Both apertures should move within the same instant.
  • Listen. A jump usually carries a small dry click. A dragging disc gives a soft whirr, or nothing at all.

If the seller will not let you watch ten minutes pass, treat that refusal as a data point.

Criterion 2: dial, apertures, and printing

Look at the frames around the two big apertures. On the original they are chamfered and finished, not stamped flat. Printing under a loupe should be crisp with no doubling, no smudging, and no orange-peel texture in the lacquer. Numeral weights and the small seconds scale should read thin and precise; replicas often use a heavier typeface that looks bolder from arm's length. Check the country-of-origin marking and the brand signature for correct spacing. A dial printed slightly too dark or too glossy is a common tell on first-copy builds.

Criterion 3: case, crystal, and finishing

A Zeitwerk case sits at roughly 42 mm across, and it is worth carrying calipers rather than trusting a description. Genuine finishing shows hand-laid bevels with sharp, straight edges where satin flanks meet polished surfaces. Replica cases typically show rounded, soft bevels and a mirror polish that bleeds over the edges. Run a fingernail along the lug facets: originals bite, replicas glide. The sapphire should be clear with a slight dome and no doubled reflection at the edge, and the crown should be engraved with enough depth to catch light.

Criterion 4: the movement side

Untreated German silver on the three-quarter plate has a warm gray tone and dulls slowly with age. Replica plates are usually rhodium-plated brass: bright, cold, and stamped rather than finished. Hand engraving on the balance cock has depth and small irregularity, because a person cut it. Laser engraving is shallow and mechanically even. Screws should show polished heads with crisp slots, and jewels should sit in gold settings on the higher-grade work rather than pressed into plain holes. Compare the serial on the caseback with the one engraved on the movement. They should match, and the engraving should look cut, not burned.

Option 1: in-hand inspection

This is the only method that answers the mechanism question, because you can time the jump yourself.

Pros

  • You can observe ten or more minute changes and the hour change.
  • Calipers, a loupe, and a fingernail test all work on the spot.
  • Sound gives you a second signal that photos cannot carry.

Cons

  • Requires travel, a meeting, or a return window you can actually use.
  • Pressure in a face-to-face deal pushes buyers to decide too fast.
  • A good case can hide a bad movement, so you still need the back open.

Use this route when the asking price is high enough that a mistake would sting, and bring a watchmaker if you can.

Option 2: photo and video review

Remote buying relies on someone else's camera, so ask for specific shots instead of accepting what is offered.

Pros

  • Fast, cheap, and useful for filtering out obvious junk before you travel.
  • A short video of the minute changing exposes a dragging display.
  • Macro photos reveal printing weight, bevel quality, and engraving depth.

Cons

  • Lighting, angle, and editing flatter bad finishing.
  • Sellers reuse stock images from other listings.
  • Still images cannot show whether the jump is instant or soft.

Use this route for shortlisting only, and request a video with the seconds hand visible next to the minute aperture.

Option 3: paperwork and provenance

Documents support a story. They do not verify a watch, and counterfeit packaging is easy to produce in quantity.

Pros

  • Service records and original papers explain gaps and confirm ownership history.
  • Serial numbers on papers can be cross-checked against the caseback and movement.
  • A dealer with a return policy gives you a practical exit.

Cons

  • Boxes, manuals, and cards are routinely faked and routinely mismatched.
  • Papers are transferable, so they often belong to a different watch.
  • Nobody services a counterfeit, which means no parts and no future repairs.

Use this route as a tiebreaker after the physical checks, never as the reason to buy.

Checklist before you commit

  1. Verify the reference number against the maker's published list.
  2. Time the minute jump for ten minutes.
  3. Watch the hour change at the top of the hour.
  4. Check digit alignment inside both apertures.
  5. Measure the case and inspect the bevels with a fingernail.
  6. Open the back for plate color, engraving depth, and screw finish.
  7. Match the serial across caseback, movement, and papers.
  8. Confirm the return window in writing before payment.

Bottom line

Start with the jump, because it is the one part of a Zeitwerk that cannot be faked cheaply, then work outward through printing, case finishing, and the movement. The number 306.104 is a claim to check, not a verdict. If the display drags, the case bevels roll over, or the plate looks like bright plated brass, the rest of the inspection has already told you what you needed to know.