In addition to their general purpose math rules, Pickett built a bunch of special-purpose rules, like this one and the N515-T. These were frequently made to order for some particular company, and stamped with that company's logo. In the case of this hydraulics and pump-efficiency rule, the case and rule are marked "Georgia Iron Works". I have no idea whatsoever how this rule is used, but boy, it's pretty big and cool, huh? The scales include such fascinating units as "Impeller Diameter", "% Solids", and "Head".