This round slider rule is marked Nestler, comes in it’s complete vinyl case that also includes a manual. Made in Germany in Bonn (DDR – Eastern Germany around 1960 when during the cold war everyone was talking about radiation and nuclear bombs. Fully functioning and in very good condition, only small signs of use or age. Diameter of the disk is ca. 10,5 cm or 4 1/4 inches wide Check the attached video on how to work your vintage man tool : slide rule operation instructions!