Dial case and movement signed. DIAM. 42 mm. THICKNESS 12 mm. FOOTNOTE TKTKTKTK Production of reference 2438 began in 1952 and ceased in 1963. Reference 2438 is similar in design to reference 2497 uses the same 27-SC Q caliber movement but was designed with a water resistant case back. It is the only vintage perpetual calendar watch made by the firm to feature a screw back. Between references 2497 and 2438 a total number of only 179 examples were produced making both models amongst the rarest perpetual calendar watches made by Patek Philippe. Both models are featured in "Patek Philippe Wristwatches" by Martin Huber and Alan Banbery 1998 pages 285-287.