As a replacement to the reference 3878, the present timepiece was introduced by Patek Philippe in 2008, and represents the skeletonized variation of its iconic Calatrava. With an impressive ultra-thin movement, the timepiece showcases the art of skeletonization as well as engraving. The caliber 240-SQU, is said to require over a week of work for the skeletonization process to be completed, with plates and bridges pieced to their maximum in order to provide the upmost aesthetical appeal. The caliber is then subject to the work of an engraver, who requires more than 130 hours for completion.