Cartier's Ballon Blue collection made its debut in 2007 with a sleek, rounded case resembling a pebble. Its standout feature is the recessed and protected crown, creating a unique "dent" on the dial. The Extra Flat 46mm was added to the line in 2011, followed by the Extra Flat 40mm at SIHH 2015. The W6920104 model boasts a 39mm pink gold case and a hand-wound caliber 9452MC with a flying tourbillon. The dial is a charming grey.