The short answer

A replica Audemars Piguet perpetual calendar sold under the code "3399" is a cosmetic copy. The dial says perpetual calendar, and from two feet away it reads that way. Under the hood you are almost certainly getting a standard automatic movement with a calendar plate or a simple triple-calendar setup, not the century-tracking calendar train that makes the real watch expensive. If you want the look and you accept that February will need babysitting, it can be a satisfying buy. If you want the function, this is the wrong product.

What the code 3399 actually is

It is not an Audemars Piguet reference. AP's perpetual calendars carry numbers like 25654, 25820 and 26574, and the modern ones run Caliber 5134, a thin micro-rotor base with a calendar module stacked on top. "3399" is a listing or factory code. Sellers recycle those codes across batches, so the same number can mean a different watch from one shop to the next. Ignore the number and judge the photographs and the movement description.

Why the movement is the hard part

Caliber 5134 sits in a case roughly 9.5mm thick and beats at 2.75 Hz with about 40 hours of reserve. That combination of thinness and complexity is what nobody has genuinely cloned at replica prices. A perpetual calendar has to know that February has 28 days, 29 in leap years, and that century years break the pattern. That is mechanical logic, not decoration, and the module that does it costs real money. Replicas get around it by using a standard movement with a calendar overlay. Some handle the 28-to-1 jump. Many do not, and just roll over like a date watch with extra windows.

Dial details that separate the tiers

  • Subdial depth. On the genuine watch the day, date and month discs sit flat under slim apertures. Replica discs often sit deeper, look milky, or land slightly off-centre.
  • Moonphase. The real disc has a textured moon on a deep blue field. Copies print a flat, pale blob that looks like a sticker.
  • Aperture edges. Look for rough filing, uneven inner rings, or printing that runs into the dial.
  • Week indicator. Later versions add a week-of-year ring. On most replicas it is decorative or tied to the date, not independent.
  • Fonts and spacing. Small text is where cheap printing shows first. Wobbly numerals, uneven month names, a date that is not centred in its window.

Case and bracelet finishing

The Royal Oak's edges do most of the talking. Real ones have crisp polished chamfers sitting on brushed flats, with sharp transitions and hex screws that sit flush. Cheaper copies have soft bevels, coarse brushing, and screws that are proud, oversized or simply slotted. Ask for a macro shot of a single bracelet link and a profile shot of the case. That pair of photos tells you more than any spec sheet.

Setting it without breaking it

Genuine AP perpetual calendars are corrected with pin tools, not by yanking the crown around. If your replica has a real calendar module, treat it the same way. Move it forward one day at a time, never backwards, and stop if it feels like it is fighting you. Push too hard on a thin module and you strip a tooth, and nobody services replica calendar modules.

Test the month change before you trust it. On the 31st it should roll to the 1st and advance the month window. If it jumps two days or skips the month, you are holding a simple calendar with a perpetual calendar dial, which is fine as long as you know that and reset it when needed.

What the tiers look like

There is a wide spread. The cheapest versions use printed dials, a stock movement and a moonphase that does not track the lunar cycle in any meaningful way. Mid tier versions fix the dial layout and add better case finishing. The top tier attempts a genuine layered dial, correct subdial positions and a module that handles short months. Price tracks those three steps, so when a listing undercuts everything around it, ask what was cut.

Quick checklist before you pay

  1. Confirmed case thickness, ideally with a photo next to a ruler.
  2. Video of the calendar rolling past a 31-day month.
  3. Macro photos of the moonphase disc and the month aperture.
  4. A clear statement of which movement is inside, and whether the calendar is a real module or an overlay.
  5. Return window in writing, and no expectation of water resistance. Do not swim or shower in it.

Bottom line

Buy the replica for the silhouette, the dial and the wrist presence. Do not buy it expecting perpetual calendar behaviour, because that is the one thing the code 3399 does not deliver. Get a seller who will send video of the month change, pay for the tier that has the dial right, and keep it away from water and from anyone who wants to argue about movement architecture.