The Speedmaster Professional is worn by astronauts in outer space. When NASA chose this watch, they requested a hesalite crystal, which "unlike a sapphire crystal" does not break into tiny fragments on impact.This feature is very important for astronauts, as the tiny fragments of a broken sapphire crystal would pose a danger in a zero-gravity environment. The Speedmaster Professional with reference number 3570.50.00 is the original Moon Watch. This model is made of stainless steel on a stainless steel bracelet, fitted with a black dial and a hesalite crystal. It is waterproof to 30 metres/100 feet and is equipped with the calibre 1861 manual-winding movement. Few things in American history have generated more interest than their nation's space program. The wrist worn Omega Speedmaster Professional (S.P.) has played an interesting role in America's conquest of space. Not only did this chronograph become famous for being the first watch worn on the moon, but the story of its selection by NASA to become the wrist timing device of the astronauts is a story of workmanship, repeated testing and a study in American politics.