Chemical calculator circular slide rule radical combiner 1936 USA

This round slider rule is made of colorful thick paper and was developed in 1936 by the Chemical Rubber Company from Ohio, USA.  It comes in its original paper sleeve with instructions on them. By selecting the non-metallic or negative part of the molecule on the inner circle and combining it with the metal radical on the outer circle it will give all information needed to make the combination compound. The diameter of the disk is a good ca. 18,5 cm or 7 1/2 inches. Everything bar some tears in the out sleeve is in great, hardly used condition. Check the below video on how to work your vintage man tool : circular slide rule operation instructions!