New calculation rule for drawing with automatic sliding device, characterized by having a graduated rule that extends inferiorly, that is, by the part opposite to the line of stroke, in a hollow body or appendix, of semicircular projection and with the tangent face to the flat and open drawing surface, serving as a housing for a cylinder that is held at its ends to the sides of the body that contains it by spikes or spikes and freely rotates inside it. (Machine-translation by Google Translate, not legally binding)
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