Stainless steel chronograph with registers Circa 1940

Stainless steel open faced lever chronograph by Patek Philippe
–
A very fine and rare Swiss stainless steel open faced chronograph keyless watch with vertical registers, circa 1940. Keyless lever movement, 23 jewels. Silvered dial with applied Arabic and baton numerals, outer tachometer scale, two subsidiary dials indicating 30 minutes register and constant seconds. Plain circular case with snap on back, two chronograph buttons in the band. Case, dial and movement signed.
–
Diameter: 45 mm
–
Signed: Patek, Philippe & Co Genève