A fake Audemars Piguet Royal Oak Perpetual Calendar usually fails on four points: case thickness, bezel screws, the Grande Tapisserie dial, and the movement behind the sapphire back. Genuine reference 26574 measures 41 mm across and about 9.5 mm thick, and nearly every counterfeit is 1 to 3 mm thicker because a cloned perpetual calendar module needs extra room. Check those four areas in that order and a replica is obvious within seconds of holding it.

What gives a fake away first?

The case profile is the fastest signal. A real 26574 is a slim watch that slides under a cuff, while replicas sit tall and top heavy, and the bracelet often hangs straighter instead of draping. Side by side, the extra millimeter is visible even from across a table.

Weight tells a similar story. Gold references use solid 18k cases and bracelets, so a genuine pink gold piece feels dense and cold, while plated brass or steel replicas feel light and thin through the links. The Swiss assay hallmark stamped inside the clasp or caseback is another quick check.

Which dial details separate real from replica?

The Grande Tapisserie grid is stamped into a solid metal dial, not printed. Genuine pyramids have sharp, crisp peaks with even depth and shadow, so the pattern shifts as you tilt the watch. Replica dials show shallow, rounded or unevenly spaced squares that look flat under direct light.

Subdial details are the second giveaway. Calendar discs, fonts, hand lengths and the moon phase disc all have to match, and counterfeits usually use generic typefaces with thicker numerals. Look at the week-of-year scale and leap-year indicator, because replicas frequently simplify or omit them.

• Hands: faceted with polished bevels and uniformly applied luminous fill, not painted flats.
• Printing: crisp AP logo and "Swiss Made" with no bleeding or uneven kerning.
• Crystal: flat sapphire with a faint blue or purple anti-reflective tint, not a domed mineral glass.

What movement belongs inside a genuine watch?

Reference 26574 runs the calibre 5134, a thin self-winding perpetual calendar movement with 374 parts, 38 jewels and about 40 hours of power reserve. It is built on the classic 2120 base with a calendar module, finished with Cotes de Geneve, circular graining and hand-bevelled bridges. The oscillating weight is solid 22k gold, so it looks warm yellow and feels heavy, while replicas use brass or plated steel.

The function test is decisive. Advance the watch to late February in a leap year and a true perpetual calendar rolls straight to February 29 without correction. Most fakes track a simplified cycle, skip the leap year, or need readjustment on March 1.

Case-side corrector pushers should also work smoothly with a slim tool, moving one indication at a time. Stiff, mushy or non-functional correctors point to a dressed-up annual or triple-calendar module.

Do the bezel screws and finishing hold up?

Eight hexagonal screws hold the octagonal bezel, and the slots on all eight line up in the same direction. Replicas rarely repeat that alignment, and their screw heads are often flat, slotted with a machine cut, or decorative rather than functional. Zoom in on a photo and the pattern is easy to see.

Finishing alternates brushed surfaces with polished bevels on the case, bezel and bracelet links. Genuine edges are sharp enough to catch light in a clean line, while counterfeits show rounded edges, wavy brushing and polishing that spills over the bevel.

How do you verify one before buying?

Match the reference and serial numbers engraved on the caseback against the paperwork, then have the watch opened by an authorized service center or qualified watchmaker. Audemars Piguet can confirm a piece through its archives, which is the only definitive answer.

Sanity-check the price. A steel 26574 trades well into five figures on the secondary market, so a four-figure asking price means replica, not bargain. Provenance, box and service history carry the rest of the story.