The names “Zerograph” and “Centrograph” were both used for watches with identical functions and bearing either reference number 3346 (with calibrated bezel) or 3462 (with milled bezel). To our knowledge this was an experimental watch produced in only a very limited number of examples for a brief period of time. It was the first “Oyster” chronograph. A similar wristwatch is published in “Rolex Collecting Modern and Vintage Wristwatches” by Osvaldo Patrizzi Guido Mondani Editore 2005 vol. II p. 120.