The tow wraps on the pivot of small diameter of pink slider. It is possible that the tow passes through a hole of the pivot. One tow end is fixed to a immobile point, the other end is fixed to a point of the green bar. Turn the bar while keeping the tow strained, the center of slider pivot traces an hyperbola.
Basic definition: Hyperbola is locus of point P moving in a plane, the difference of its distances from two fixed points is constant (the tow length).