Quick answer
33671 is a seller-side SKU, not a Cartier reference number. In listings it almost always points to the 33mm steel Ballon Bleu de Cartier with the silver textured dial, blue cabochon crown and a date at 3 o'clock. That size maps to Cartier's own reference W6920071. So when you search this number, you are shopping for a copy of that watch, not a specific factory model. The factory is usually named in the listing title anyway (AF, V6F, 3K, and so on).
What the genuine watch looks like
Steel case, 33mm across, roughly 9.9mm thick, with a domed sapphire crystal that sits a little above the bezel. The crown is capped by a blue synthetic spinel cabochon and partly hidden under the curving case flank, which is the whole design idea behind the name. The case is rated to 30 meters, and that rating is thin even on the real thing. Inside sits Cartier's calibre 076, an ETA 2671 base with a date. Dial texture is guilloché, cut in concentric rings, not printed. Hands are blued steel, sword shaped.
Where cheap copies fall apart
- Case profile. The replica case is often 1mm to 1.5mm too thick, and the crystal dome looks like a bubble instead of a gentle arc.
- The cabochon. Genuine is a deep blue dome, translucent, not a flat plastic dot. Cheap versions are cloudy or violet.
- Dial texture. Good copies cut real concentric rings. Bad ones print a wave pattern on a flat disc, and it reads as a sticker under light.
- Crown guard. The metal should wrap the crown smoothly with no gap and no sharp lip. This is the part most buyers spot first.
- Bracelet. Links should taper toward the clasp with clean alternation between brushed and polished surfaces. Loose links and a rattling clasp are the giveaway.
- Caseback engraving. Spelling, spacing and font weight. Misspelled "Swiss Made" is still common.
Movement tiers
Three things show up under this SKU. Quartz, which ticks and is the cheapest. A Miyota 9015 automatic, which is smooth and reliable but the rotor is noisy. And a decorated 076 clone on an ETA 2671 base, which is the tier most people shopping this reference actually want. Ask which one is inside before paying. If the listing does not say, assume quartz.
Size and fit
33mm wears small on a 7 inch wrist and reads almost dressy. The 36mm version wears closer to a modern everyday watch, and the 42mm is a different animal entirely. Measure your wrist before ordering and check the listed lug width, because the bracelet often cannot be swapped for a strap without extra hardware.
Water and daily care
Treat any 30 meter case as splash proof only. No swimming, no shower, no hot tub, and dry the crown area after washing your hands. Have the gaskets checked if you plan to wear it in rain regularly.
What I check on arrival
Wind it, set the date, and watch the seconds hand for a full minute. Then look at the dial straight on under a lamp, tilt it to 45 degrees, and check the cabochon under daylight. If the dial rings vanish when you tilt it, you got a printed dial. If the cabochon turns purple, it is glass, not spinel.