Ma Jun, courtesy name Deheng, was a Chinese mechanical engineer and politician who lived in the state of Cao Wei during the Three Kingdoms period of China. His most notable invention was that of the south-pointing chariot, a directional compass vehicle which actually had no magnetic function, but was operated by use of differential gears (which applies equal amount of torque to driving wheels rotating at different speeds). It is because of this revolutionary device (and other achievements) that Ma Jun is known as one of the most brilliant mechanical engineers and inventors of his day (alongside Zhang Heng of the earlier Eastern Han dynasty). The device was re-invented by many after Ma Jun, including the astronomer and mathematician Zu Chongzhi (429–500). In the later medieval dynastic periods, Ma Jun's south-pointing chariot was combined in a single device with the distance-measuring odometer.