This bar linkage function generator mechanizes the logarithm function, an interesting feature for mechanical computation. The approximation is quite good given the simplicity of the mechanism (only 3 bars).

The details on the synthesis of this mechanism can be found in the paper written by P. A. Simionescu: “A restatement of the optimum synthesis of function generators with planar four-bar and slider-crank mechanisms examples,” Int. J. Mechanisms and Robotic Systems, Vol. 3, No. 1, 2016 (DOI: 10.1504/IJMRS.2016.077038).