2 Riezt model slide rules by Aristo from their earlier productions in the 1950’s. It is the model 99 and 99k. Covered in the English booklet with large fold out pages. They are complete and show signs of use and age, sleeves are good, only the black one is signed. They measures ca. 30 cm or 12 inches long. Check the attached video on how to work your vintage man tool: slide rule operation instructions!
