Certina Art Deco 1940's

It is not until 1939 that Kurth Freres registers the brand name Certina. and we can find it on their watches. In the early years, the watches are powered by KF movements (Kurth Freres) and not yet marked Certina. Later on, the Certina marked movements appear and they carry the Incabloc shock system. My art deco watches have the KF230 resp. the KF 251 manual movements.