Graphoplex SHELL Stack loss excess air pocket slide rule 1960 Dutch France

This slide rule has been specially constructed for Shell by Graphoplex (not branded Grapoplex, but reads “Modèle Déposé in French) and has the Dutch and English language on it (there is also French/English version). The front has scales for calculating excess air and CO2. On the back stack loss for oil fuel burning. The slider has a Dutch and an English side, all other text is in Dutch. It also comes in the original SHELL signed leather sleeve. The interesting dedicated curser, rule and sleeve are complete and in very good condition. with minimal signs of use and age. It measures 19 cm or 11 1/2 inches. Do check the attached video on how to work your vintage man tool : slide rule operation instructions!