Graphoplex Texaco 615 oil industry pocket slide rule 1960 France

This slide rule has been specially constructed  by Graphoplex and is based on the standard 615 model. But this one has a unique cursor shape with diagonal hairlines as well as oil viscosity by different temperature. To this end there is an extra scale set in the stock and a table on the back. The back of the slide has additional scales as well. This model has been sold in small batches to different oil production companies. Besides this Texaco example in origine Texaco printed leather sleeve, I also saw a model for Caltex and Calcrude oil. The interesting dedicated curser, rule and sleeve are complete and in very good condition, with minimal signs of use and age. It measures 18 cm or 9 1/4 inches. Do check the attached video on how to work your vintage man tool : slide rule operation instructions!