In the 1930s and 1940s the so-called observation watches were an essential part of a pilot’s equipment. This observation watch served as a means of navigation in addition to the cockpit instruments compass and altimeter during the visual flights common at that time with previously fixed routes and turning points. Before the start of a flying squadron the crowns of the watches were pulled out and the watches were set to zero. When the captain gave the order "Start" the crowns were pulled in so that the watches of each pilots were running synchronously. After a certain fixed time an order previously determined could be performed. It was very important that the mechanical watch movements had to be of highest precision. The technical features of these watches were specified by the Reichs-Luftfahrt-Ministerium (ministry for aviation). The shape of the hands , the design of the dial, the typeface and also the dimension of the crown were defined by this ministry.
The number “12” on the dial, marked with an arrow, enabled the pilot to get a fast orientation in each situation, and by means of the disproportional big crown the watch could be handled without having to remove the gloves. In order to ensure that the dial could be read during night the hands and the numbers on the dial were equipped with radium, a radioactive material with high luminosity. These observation watches were classified with “FL23883”, a description for navigation instruments. This number was engraved on the outside of the case, on the opposite side of the crown.
Due to the high standard concerning precision and reliability the production of the observation watches was a great challenge for the watch manufacturers. In the 1930s and 1940s, only five companies were authorized to produce such observation watches: IWC in Schaffhausen, Lange + Söhne in Glashütte, Wempe in Hamburg, and Stowa and Laco (Lacher & Co.) in Pforzheim. From these five companies only two (Lange + Söhne and Laco) used movements of their own production. The other three companies used Swiss movements.
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