Ref. 2499Produced in 349 examples from 1951 to 1985, very few with tachometer, the majority in yellow gold, and a very few examples in pink gold.- First series: from 1951 to circa 1960, square buttons, "Feuille" hands, applied Arabic numerals, fluted lugs. It is extremely rare in this series to find models with dials differing from the above; in particular, no watches with black dials are known.- Second series: square buttons, "Dauphine" hands, applied indexes, the 12 in Arabic numerals. No watches with black dials are known in this series.- Third series: from 1960 to 1978, round buttons, crystal glass, "Dauphine" or "Feuille" hands, applied "bâton" indexes. In this series, only four watches with black dials are known.Only one split-seconds chronograph with waterproof case is known bearing this reference, specially made by Patek Philippe for Gobbi, Milano, in 1982.Ref. 2499/100:- Fourth series: From 1978 to circa 1985, round buttons, sapphire crystal, "Dauphine" hands, applied "bâton" indexes. Very few examples were made with tachometer or telemeter scale and three pieces only with sapphire crystal back. In this series, models with the tachometer indication are extremely rare. Only one example is known with a black dial. This reference was produced in: yellow gold and in pink gold, and only two examples in platinum, of which one was sold by Antiquorum in Geneva on Apri9, 1989, "The Art of Patek Philippe", lot 34, for SFr. 418'000 (US$ 253,300).A similar watch is published in "Patek Philippe Wristwatches", by Martin Huber and Alan Banbery, 1998, page 302 and in "Collecting Patek Philippe Watches" by M. and O. Patrizzi, Guido Mondani Editore, Genova, 2000, p. 296, pl. 476A.