Simon Stevin's work in the "waterstaet" involved improvements to the sluices and spillways to control flooding. Windmills were already in use to pump the water out, but in "Van de Molens" ("On mills"), he suggested improvements, including the idea that the wheels should move slowly, and a better system for meshing of the gear teeth. These improvements increased the efficiency of the windmills used to pump water out of the polders by three times. He received a patent on his innovation in 1586.