From Chuck Maddox's incredible cache of knowledge, www.chronomaddox.com;
"In 1972, Lemania and Omega presented their jointly developed caliber 1040a central rotor winding automatic chronograph with a diameter of 13 3/4 lines, and a height was 8 mm. The Mark III marks the first use of this movement in an Omega watch. The Omega c.1040 movement is a non-chronometer rated movement. However in 1973 after some fine tuning the chronometer grade c.1041 movement used in the Speedmaster 125 Anniversary Chronograph would be produced.. Both Omega Calibre 1040 and 1041 are also known as the Lemania Calibre 1341. The 125 marked Omega's first Chronometer Chronograph, and was the first chronometer grade automatic chronograph. a precursor to the current Seamaster Professional Chronograph-Chronometer, although the movement has little in common with the current model Seamaster."
My Cal 1040 is a Speedmaster Seamaster Professional Automatic, making it post 1973. This is a model I lusted after for a long while, and it is every bit the machine I thought it would be. It has been dunked into Sydney Harbour from a capsizing Kayak, and lives to tell the tale….