Alro military army circular slide rule in leather pouch 1950 Holland

This round slide rule is marked ALRO Militaire Rekenschijf (army circular slide rule). Made in Holland in The Hague around 1950. Very rare model, issued to the Dutch army only for calculating angels of fire specifically for mortars and other large artillery fire. High quality build with metal ring on a very thick black early plastic back ground with yellow inlay (explanation on use). In good working condition with signs of use and age (little wobble on the inner ring) and. fully functioning. It comes the original heavy duty leather case that is complete and in very good condition as well. It measures ca 13 cm or 5 1/4 inches in diameter. See pictures for details. Check the attached video on how to work your vintage man tool : slide rule operation instructions!