A mechanism to trace ellipses which uses two concentric circles of radii a(AB) and b(AC) to create the ellipse with these axes ( c = sqrt(a^2 - b^2) = |AI|). The shape of the ellipse is controlled by the two points D and E. The geometry of the figure is discussed in the file Ellipse_Construction.html .

The circle with diameter GE is the [Auxiliary] circle of the ellipse. It is discussed in Auxiliary.html .

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