 It was completed in 1412, a long while after Liu's death, with a preface added by the Jiao in its Nanyang publication.Although an ancient hematite artifact from the Olmec era in Mexico dating to roughly 1000 BC indicates the possible use of the lodestone compass long before it was described in China, the Olmecs did not have iron which the Chinese would discover could be magnetised by contact with lodestone.Descriptions of lodestone attracting iron were made in the "Guanzi", "Master Lu's Spring and Autumn Annals" and "Huainanzi".