Guidonian hand
In Medieval music, the Guidonian hand was a mnemonic device used to assist singers in learning to sight-sing. Some form of the device may have been used by Guido of Arezzo, a medieval music theorist who wrote a number of treatises, including one instructing singers in sightreading. The hand occurs in some manuscripts before Guido's time as a tool to find the semitone; it does not have the depicted form until the 12th century. Sigebertus Gemblacensis in 1105–10 did describe Guido using the joints of the hand to aid in teaching his hexachord. The Guidonian hand is closely linked with Guido's new ideas about how to learn music, including the use of hexachords, and the first known Western use of solfege.
Hand cannon
Hand cannons first saw widespread usage in China sometime during the 13th century and spread from there to the rest of the world. In 1287 Yuan Jurchen troops deployed hand cannons in putting down a rebellion by the Mongol prince Nayan. The earliest artistic depiction of a hand cannon – a rock sculpture found among the Dazu Rock Carvings – is dated to 1128, earlier than any recorded or precisely dated archaeological samples, so it is possible that the concept of a cannon-like firearm has existed since the 12th century. The oldest extant hand cannon bearing a date of production is the Xanadu Gun, dated to 1298. The Heilongjiang hand cannon has been dated to no later than 1288, but this dating is based on contextual evidence; the gun bears no inscription or era date. Other specimens also likely predate the Xanadu and Heilongjiang guns and have been traced back to the Western Xia period, but these too lack inscriptions and era dates.