Dial case and movement signed. DIAM. 35 mm. THICKNESS 9 mm. Property of the Original Swiss Owner Production started in 1958 first with the caliber 12-400 and from 1960 with the caliber 27-400. These calibers are equipped with a bronze-beryllium lever escapement and are fully protected by a soft iron cap.They are impervious to magnetic fields up to 450 oersteds (unit of measurement of the intensity of a magnetic field). A similar watch is published in "Patek Philippe Genève Wristwatches" by Martin Huber and Alan Banbery1998 Edition pp. 192 and 194. This example was gifted to the father of the current owner and has been maintained in excellent all original condition with a nice crisp hallmark to the side of the case. Much rarer than its stainless steel counterpart the gold versions were made in a limited production and this dial configuration featuring only an arabic 12 rather than the arabic quarter hours is the rarest configuration Antiquorum having only offered 2 other similar examples in the last 27 years.