Jeffers Calculator, American ready reckoner for nutritive ratios, by Henry Jeffers, 1907

Like the triangular rule, this instrument is for someone who loved figures. Henry Jeffers was a New England dairyman and republican politician. He devised this ready reckoner in 1907 to compute the right mixtures of feed and ingredients for livestock nutrition. About 60 slides, each for a different animal foodstuff, can be slid into the ‘calculator’ on the right-hand side of the open box. For any number of pound weight, the dry matter, ‘proteids’, carbohydrate and fat can be read off. There is also a cost calculator.