The art of haute horology is that of combining mechanical precision with complications. It is a challenge to make the two coexist; generally speaking, complications interfere with the precision of the watch, due to the additional parts. To maintain a high level of precision and overcome the resistance of the additional springs, racks, levers and wheels of a watch with minute-repeat, calendar and moon phases, like the present watch, requires a level of precision that a select few have been able to achieve. Throughout the history of horology, very few master watchmakers have attempted to create complicated watches with detent escapements. Patek made their first chronometer watches with complications around 1844, (the serial numbers are below 10,000, and fewer than ten are known to exist), all with spring detent escapement and quarter-repeat. During the following 90 years, very few complicated watches with chronometer escapements were made. The next significant achievement in this field w s at the end of the 1980s, when Patek Philippe launched a series of ultra-precision complicated watches, reference 961, employing a detent escapement. A total of two are known to us in yellow gold, of which the present watch is the second. The first was sold by Antiquorum in the ?Private Collection of Theodore Beyer? sale in Zurich, on November 16, 2003, as lot 153. This series places Patek Philippe at the forefront of a group of less than a dozen horological masters who have attained this milestone since the detent escapement was invented.