Wujing Zongyao
Since the time of the engineer and inventor Ma Jun (c. 200–265), the Chinese had used the south-pointing chariot, which did not employ magnetism, as a compass. In 1044 the "Collection of the Most Important Military Techniques" (; "Wujing Zongyao") recorded that fish-shaped objects cut from sheet iron, magnetized by thermoremanence (essentially, heating that produced weak magnetic force), and placed in a water-filled bowl enclosed by a box were used for directional pathfinding alongside the south-pointing chariot.