In 2007, Cartier launched their Ballon Blue collection. The watches have a sleek, rounded case that resembles a pebble. A standout feature is the protected crown that creates a slight dent on the dial. One model, the WSBB0015, has a stainless steel case coated in black ADLC and a black dial. It's also one of the first Ballon Bleu watches to use Cartier's own caliber 1847 MC movement.