As a side note, despite the 1929 merge, Deuta still exists as a separate company. And also, even in the 1930s and WW2 there were VDO instruments, but in the same time there were Deuta instruments, too. For example, various Luftwaffe instruments are marked Deuta Werke, no mention of VDO. Strange it is.
Regarding this speedometer, this is how I narrow its use: it shows speed, so it is for a vehicle, not for a static machine. May not be a tank or agriculture tractor, too fast. Probably not a car, too, showing just 80 km and the instrument is too large and heavy. My guess would be either a truck, or a diesel locomotive. But do locomotives have that kind of gears, 4 gears, I am not familiar.