The Eratosthenes’
mesolabe (mean-taker)

It is a most brilliant tool that was invented by Eratosthenes in order to achieve the interjection of two or more proportional means between two given line segments. With this way it was achieved also the solution of the Delian problem that concerned the doubling of cube. They were constituted by a rectangle frame in form of “Π” with a stable rectangle triangle and two or more sliding rectangles or triangles on uneven grooves inside the frame.