Commentary on the Record of Trades, Volume 1

The Wheelwright Che-ren: the specific craftsman responsible for the chassis and wheels records that for traveling through marshlands, one desires a short hub gu: the central part of the wheel through which the axle passes; for traveling through mountains, one desires a long hub. In the case of a large cart, the hub's length is half a measure original: 柯 (ke), an ancient unit of measurement based on the length of an axe-handle, approximately 3 feet., and its circumference is one and a half measures. This implies that if a hub is short, its circumference must necessarily be small. For a cedar-wood cart, the hub's length is one measure and its circumference is two measures. This implies that if the hub is long, its circumference must necessarily be large. If the hub is long but the circumference is small, or the hub is short but the circumference is large, then the proportions are mismatched and the vehicle will not travel effectively. Although this record specifically discusses the hubs of a four-horse carriage, the technical principles apply universally.

The Woodworker Zi: the master craftsman specializing in precision carving and lacquering lacquers the interior of the hub and creates a curve in its center; this determines the hub's length, and that length is then used to determine the circumference.

The Records of the Grand Historian original: 史記 (Shiji), the foundational history of ancient China by Sima Qian. in the "Treatise on the Balanced Standard" states that when the Five-Zhu coins wuzhuqian: the standard bronze currency of the Han Dynasty were recast, they were given a raised perimeter original: 郭 (guo), usually meaning a city wall, but here referring to the protective rim of a coin. so that people could not file away the edges to steal the metal. It appears that in ancient speech, the term for a "surrounding boundary" was guo, and the usage of perimeter by the Woodworker carries the exact same meaning.