Originally, all books were in manuscript form. In China, and later other parts of East Asia, woodblock printing was used for books from about the 7th century. The earliest dated example is the Diamond Sutra of 868. In the Islamic world and the West, all books were in manuscript until the introduction of movable type printing in about 1450. Manuscript copying of books continued for a least a century, as printing remained expensive. Private or government documents remained hand-written until the invention of the typewriter in the late 19th century. Because of the likelihood of errors being introduced each time a manuscript was copied, the filiation of different versions of the same text is a fundamental part of the study and criticism of all texts that have been transmitted in manuscript.