If practice makes perfect, do supply curve slope up? As Adam Smith had predicted, most production processes are characterized by learning by doing with increasing efficiency over time and with the experience. In the production of liberty ships during World War II, for example (see the graph to the left), the labor required to build a ship fell by as much as two thirds over less than four years because experience allowed workers and engineers to become better at building ships and to figure out better ways to organize production. Can you draw a marginal cost curve for a firm where productivity increases with output?, Do supply curve slope up