A large circular slide rule with 2 cursors resembling the hands of the clock, specially designed for viscosity related calculations, rustling in the name “Visco-klok) (Dutch for “clock”). Made by ARO from The Hague (Holland) for the Dutch oil company Shell (still has its headquarters in The Hague). The slide rule is in great condition and comes in the original vinyl folding sleeve (taped on spine). The manual is missing but there is an English translation online available here. The slide rule measures ca. 18,5 cm or ca. 7 1/2 inches in diameter. Check the attached video on how to work your vintage man tool : slide rule operation instructions!
