This instrument, developed by Giovanni Battista Suardi in 1752 and perfected by Felice Gori, is similar to the one depicted by George Adams in his Geometrical and Graphical Essays (London, 1791). It is used to trace a large variety of curves generated by combining several rotating motions. A vertical axle with a revolving arm pivots at the center of a tripod support. The revolving arm carries a second pivoting arm fitted with a writing tip. Thanks to a series of gearwheels, the rotation of the two arms generates complex cycloidal curves. The instrument case contains the gearwheels, which can be combined to change the arm-rotation ratios and, consequently, the plotted curves.