This round slider rule is marked ALRO Syst 300D, comes in it’s complete metal case. Made in Holland in The Hague around 1950 after the patents were received. Rare model in good working condition with hardly any signs of use and age. Fully functioning. Closed it measures ca 13,5 cm or 5 3/8 inches wide. See pictures for details. Check the attached video on how to work your vintage man tool : slide rule operation instructions!
