Faber Castell 67/87R addiator pen slide rule full set 1970 Germany

This is a great transitional and unusual Faber Castell slide rule that has a double function. It is a combination of slide rule in Rietz format on one side and an addiator on the other side. The addiator is a predecessor of the basic handheld calculator (as is the abacus) with function that allows for quick addition and subtraction of amounts. The slide rule itself is more the predecessor of the scientific electronic calculator. This pocket version is based on the Faber Castell 67/87 (see also manual in German) and is now called the or or 67/87 R (see case) or 67/87 Rb (see slide rule). It comes complete with the pen and the original green leather sleeve with Faber Castell logo. Very nice set in good condition with only signs of normal use and age (minimal sun yellowing on one end) and a small water stain on manual. It measures ca. 16 cm or ca. 6 1/4 inches. Check the attached video on how to work your vintage man tool : slide rule operation instructions!