This Patek Philippe Perpetual Calendar Chronograph Ref 3970EG-020 is rated 9.7 out of 10. It comes with box, back case and certificate dated in August 2003. With a total production of around 4000 pieces for the 3970 reference, there are 3 series in existence. Of the 4000 pieces, the black dial, white gold version is considered the ultimate 3970, as it is the rarest, and hence highly collectible.