What a sketched mechanism costs

A four-bar positioned the way one is drawn by hand: the crank pin at its angle, and the rocker interpolated smoothly between its extremes because that is what the motion looks like. Plotted is how long the coupler would have to be at each position, minus how long it is. The error reaches 0.89 on a coupler of 3.5 — 25% — and a reader looking at the drawing would see nothing wrong, because every individual frame is a perfectly plausible picture of a four-bar. This is the failure the solver exists to make impossible: a configuration that does not satisfy the constraints cannot be drawn, because there is nothing to draw it from.