The W69012Z4 is the 42 mm steel Ballon Bleu de Cartier, one of the versions with which Cartier introduced the Ballon Bleu in 2007. The round, domed case is the starting point of the design; its most striking detail is the crown, which is set into the case and protected by a steel guard.
The crown carries a blue cabochon, from which the model takes its name. The silvered dial is guilloché, with Roman numerals and blued steel sword hands.
Inside is the automatic calibre 049, with date. The watch comes on a steel bracelet with a folding clasp.
On a pre-owned example we look above all at the guard around the crown, which is the first place to pick up dents or scratches from a knock, and at the cabochon itself.
We also examine the domed sapphire crystal, the guilloché and the date, the bracelet with its folding clasp and the polished flanks of the case. We compare the serial number on the caseback with the guarantee card and test winding, setting and timekeeping.
How we assess a watch before making a proposal is explained in our guide to having a watch valued.