Polymath personalities – that is, people knowledgeable across an encyclopaedic range of topics – such as Shen Kuo (1031–1095) and Su Song (1020–1101) embodied the spirit of early empirical science and technology in the Song era. Shen is famous for discovering the concept of true north and magnetic declination towards the North Pole by calculating a more accurate measurement of the astronomical meridian, and fixed the calculated position of the pole star that had shifted over the centuries.[3] This allowed sailors to navigate the seas more accurately with the magnetic needle compass, also first described by Shen.[3]