Cartier's Ballon Blue collection made its debut back in 2007, sporting a sleek and rounded case. One distinctive feature is the recessed and shielded crown, creating a unique "dent" on the dial. The Extra Flat 46mm joined the lineup in 2011, followed by the Extra Flat 40mm at SIHH 2015. The reference W6920105 stands out with its 39mm white gold case, home to the hand-wound caliber 9452MC and its flying tourbillon. The charming blue translucent enamel covers the guilloché dial.