Quick answer

If you are shopping for a replica Cartier Tank Must in yellow gold, you are chasing a small, thin quartz dress watch with a solid gold case on the real thing. Most replicas nail the outline and miss the finish. Three things decide whether one is worth your money: case thickness in profile, the blue cabochon in the crown, and the quality of the dial print. Get those right and the movement is almost an afterthought, because quartz is quartz.

What the genuine Tank Must in yellow gold actually is

Cartier sells the Tank Must in 18K yellow gold in the large size, about 33.7 mm by 25.5 mm, with a quartz caliber inside. The dial is silvered opaline with Roman numerals, a chemin de fer minute track, the wordmark printed under the 12, and SWISS MADE at 6. The crown is fluted and set with a blue spinel cabochon. Crystal is sapphire, and the strap is alligator with a gold ardillon buckle. If your search for yellow means a yellow dial rather than a yellow gold case, you are looking at a different reference, and it changes what you should compare.

Case and plating: where replicas give themselves away

Almost every replica is gold plated steel, not solid gold. The better ones run 3 to 5 microns of plating, which is enough to survive a few years of careful wear. Turn the watch in your hand and look at the lug tips, the crown side, and the caseback edge, because that is where plating thins first and where a paler steel rim shows through. A magnet will jump to a plated steel case and will not cling to a solid gold one, which is the fastest sanity check you can run.

• Thickness. The genuine case sits near 6.6 mm. Many replicas add a millimeter or more, and you feel it in profile on the wrist.
• Color. 18K yellow gold reads warm and slightly soft. Brass-heavy plating reads green or harsh.
• Caseback engraving. Reference numbers should be cut with depth and a clean font, not laser-etched flat.
• Lugs. The Tank case tapers into slim, straight lugs. Fatter lugs with rounded edges are a common miss.

The dial is the hard part

At 25 mm wide, the dial print is tiny, which is exactly why it exposes cheap work. Check the Roman numerals for even stroke weight and sharp serifs. The minute track should be fine and consistent all the way around, with no blotching where the two lines meet. Hands on the gold model should be a crisp sword shape with a clean finish, and the wordmark under the 12 should be legible under a loupe without looking bold or clumped. Some Cartier references hide a signature inside a numeral. The Tank Must does not, so a seller advertising that detail is describing something else.

Crown and cabochon

The genuine blue spinel is faceted and translucent, set into a fluted crown that turns smoothly. Replicas use dyed glass, plastic, or synthetic stone, and the flaws show under direct light. Real spinel shifts tone as you tilt it. Glass sits flat, often too dark or too uniform. Look at the crown teeth as well. They should be evenly cut and match the case metal, not chromed steel standing next to a gold case.

Movement and crystal

Both the genuine watch and the replica are quartz, so timekeeping will not tell you much. The genuine uses a Cartier quartz caliber. Replicas use Ronda, Miyota, or unbranded Chinese modules, and a sweeping seconds hand is not a feature to expect here because the real watch ticks once per second too. If a seller advertises a Swiss movement, ask for the caliber number. For the crystal, sapphire will shrug off a rub with a steel key while mineral glass will not, and that difference matters more on a dress watch you will bang against doorframes.

Strap and buckle

Genuine straps are alligator with a signed gold ardillon buckle. Replica straps are usually embossed calf, which is fine to wear but easy to spot next to the real thing. Look at the buckle engraving depth and the pin shape. A thin pin with shallow lettering is a giveaway, and it is also the part that fails first.

Price bands and what they buy

• Under $80: thin plating, plastic cabochon, soft dial print. Wearable as a knockaround piece, nothing more.
• $150 to $350: the sensible zone. Decent 3 to 5 micron plating, sapphire crystal, clean dial, reliable quartz.
• $400 to $700: tighter case tolerances, better dial finishing, sometimes a real leather strap.
• Above $1,000: solid gold or gold-capped cases. Ask for weight and plating thickness before you commit.

Living with a plated case

Sweat, perfume, sunscreen, and hand lotion all eat plating. Wipe the case with a soft cloth after wear and keep it away from the pool. Never polish a plated case with an abrasive cloth, because you will burn through the gold layer in one sitting. If the plating does wear at the lugs, a jeweler can replate the case, and that cost is worth weighing against what you paid.

Before you pay

Ask for photos in daylight, at an angle, and on a wrist. Request caliper shots of the case thickness and the lug width so you can compare them to the reference specs. Confirm sapphire crystal and plating thickness in writing. Buy from a seller with a return window, and inspect the crown action and cabochon the moment it arrives, since those are the two details a photo will not fully reveal.