My question is based on the information that appears in several websites, according to which I found three examples of a kind of instrument that was probably an analog computer. The first one mentioned, which is from the great soviet encyclopedia (so I suspect it might not be true), is a kind a integrator, i.e, a machine that can solve differential equations. The second instrument is from wikipedia article here and it's supposedly a drawing machine. The third one is reported by Couturat and was a kind of an algebraic calculator, i.e, a calculator that can perform algebraic operations. And I have to mention another source which states: "Many other elementary analog devices were described before the modern period: Differential gears (Figure 1). used for adding or subtracting two variables. arc usually ascribed to Leonardo da Vinci: and Leibniz is credited for the idea late in the seventeenth century of a similar-triangles device for equation solving or root solving"
So can anyone offer explanation of the underlying principle of this instruments? and mayby even offer explanation of their inner-workings?