Rare stopwatch of the German Imperial Air Force Circa 1916

Gunmetal stopwatch by F.W. Kreis
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A rare German gunmetal stopwatch the Imperial Air Force used in World War I, circa 1916. Bridge movement, a lever escapement and monometallic screwed balance.
Printed white enamel dial with an Arabic 1, 2 and 3, one hand. The plain case is engraved with a propeller and FLZ.
Dial signed.
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Diameter: 52 mm
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Weight: 101 g
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Signed: F.W. Kreis – Berlin W.
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Dr. Konrad Knirim states in this context:
This particular stopwatch was used by the Imperial Aviation Units during the First World War. The marks showing a winged propeller with the letters PuW or Flz are quite commonly used on the Imperial Air Force timepieces, often in combination with full owner’s identification. Around 1916, the Flugzeugmeisterei (FLZ) (Air Force maintenance unit) at Berlin Adlershof was formed from the Prüfanstalt und Werft (PuW) (the Testing and Service divisions). The FLZ at Adlershof still existed during the Second World War. One revolution of the central second equates to three minutes and after each revolution, a colour change takes place to red, green or yellow, at zero position, there is no colour change. The timepieces were used during the warm-up phase of the aeroplane engines. There is, however, no original documentation on how the watches were used. The watches were converted and delivered by the watch dealer and jeweller Friedrich Wilhelm Kreis in West Berlin, who supplied a great number of pocket chronographs and stopwatches. The movement is most likely a converted Lemania 19Np.
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Friedrich Wilhelm Kreis owned the company Strasser & Rohde from 1918 until his death and moved it from Glashütte to Berlin.