in 1970, tudor released its first chronograph, the oysterdate, with a manually-wound valjoux mechanical calibre 7734 and a cam mechanism chronograph function. the second series, introduced in 1971, was nicknamed the "montecarlo" because the dial resembles a casino roulette wheel. the third series, the oysterdate "big block", were the first tudor chronographs to introduce a self-winding movement in 1976. the tudor monarch collection was launched in 1991, and the tudor hydronaut in 1999.