This type of compass has quite a story.
Two companies produced it, o/y Physics A/B Helsinki and Suunto Helsinki. Developed for the Finnish army before 1940, the Germans used it in WW2 as a paratrooper wrist compass. After the war it was sold by the ANWB (an organisation like the AAA in the US and the AA in Great Britain) in the Netherlands to their members (This compass was sold in 1948.) This compass was delivered in a carton box under the name "Armatikon". You can also see the logo of the ANWB.
It has still the German tekst on the back of the compass and the manual is also in German. Titel of the manual is: "Marsch-Kompass P1 einteilung 6400"
The mirror is special, I never saw it on this type of compasses.