Some mathematics for the plotter
 

 For this purpose we have to transform Cartesian coordinates to polar-coordinates.

 

The precision of drawing depends on several factors. The most important seems to be the length z. z will amplify any deviation at the point (0,0), produced for mechanical reason.  A deviation of 1 degree produces an arc of Pi/180 cm= 0,17 mm at a distance of 1 cm from the origin. This deviation will produce an arc of  0,44 cm (!) at a distance of 25 cm which is about the largest z. So this plotter will render a result with a certain not negligible error.

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