The watch Donald Draper is wearing in Season 7 Episode 3 is an Omega Seamaster DeVille (also seen in Season 6). This timepiece has an automatic movement. The model was equipped with either caliber 562 or 563.
The 562 was a 24 jewel movement that began production around 1958. Caliber 563 was introduced around 1965 with 17 jewels. The diameter of this vintage piece is a classy 34.5mm and takes an 18mm strap.