The diamond forming the watch crystal in this piece is exceptionally rare, as it is extremely difficult to find such a large and pure diamond crystal from which it had to have been eut. Apart from it's incredible size and purity, the cutting of this store, being one of most difficult nits to polish, is another impressive aspect of this finely made piece. Designed as a special commission, only 4 of these wristwatches were ever made, each one different from the next; one was made with sapphires, one with rubies, one with diamonds and one with emeralds. Equally noteworthy is the fact that skeletonized movements are uncommon in Cartier's writswatches and these octagonally shaped movements were specially made for these four. The sapphire watch and the diamond watch are, therefore, unique and are extremely rare and collectable.