The Rolleiflex standard was produced by the Franke & Heidecke company in a German town, Braunschweig between 1932 and 1938. The camera is referred as the Rolleiflex Old Standard. This name is not the actual type name rather it became known by this name after the introduction of the Rolleiflex New Standard model in 1939. The famous war photographer Robert Capa also used this model and a Contax during the World War II.
The Rolleiflex waist level finder had a built-in Libelle. Please see attached images.
The sportsfinder is designed to be able to position the object in the center of your photograph, by looking through the opening you could see a cross with a small mirror in the middle. The iris of your eye is reflected in the mirror.