The Beobachtungsuhr — B-Uhr in common parlance — was not a pilot's watch in the sporting sense of the term: it was a navigation instrument worn on the wrist, commissioned by the Reichsluftfahrtministerium starting in 1940 from five German and Austrian watchmakers. Stova, Laco, A. Lange & Söhne, IWC, and Wempe responded to the same technical specifications, which explains why the original examples resemble each other so closely despite coming from different manufacturers.
The dimensions were imposed by the task at hand: 55 mm case diameter, thickness around 16.5 mm, weight exceeding 180 grams. Inside lived a manual-wind movement derived from pocket watch calibers, chosen for chronometric precision rather than compactness. The oversized onion crown allowed for adjustment even while wearing flight gloves at altitude.
The dial followed a logic of absolute readability: opaque black background, large white Arabic numerals, broad hands with luminescent treatment. The most recognizable detail is the triangle at 12 o'clock, flanked by two circular dots: a rapid orientation system that allowed one to read twelve even in poor lighting conditions or with partially obstructed visibility.
In 1942, two official variants appeared. The Baumuster A maintained the original layout with Arabic indices across the entire surface. The Baumuster B inverted the visual hierarchy: a broad minutes scale on the outer edge of the dial, and a smaller circle for the hours inside, with an arrow in place of the triangle at 12 o'clock. The Baumuster B is less common among surviving originals, and it is the one collectors seek most insistently.
From my workbench I have seen very few authentic examples in good condition pass through: the cases were large but the finishing was military, not refined, and the dials tend to separate. Modern revivals — IWC Big Pilot, Stowa Flieger, Laco Pilot — take up the visual vocabulary with varying fidelity, but none replicate the original dimensions without some commercial compromise. The triangle at 12 o'clock has become the hallmark of the entire pilot watch genre, even when the historical connection is merely decorative.