Yanling Dao developed from straight back Dao in Qin and Han Dynasties to Song Dynasty, and even spread to Mongolia. As the name implies, the blade is straight and sharp, but from the Yanling knife, the blade gradually bends. The earliest existing Yanling Dao can be traced back to the Ming Dynasty, and it was not widely used until the late18th century after textual research.
In the process of development, Qing Dao and The Lancet further popularized the concept of Yanling in the radian of the blade, because the blade tip and the blade back are not on a horizontal line at all. Interestingly, the greater the curvature of the blade, the more obvious the cutting effect of the knife, but the corresponding pricking accuracy will decrease, because the tip is farther from the handle. However, The Lancet's radian is moderate, even if its accuracy is slightly lower, it is better than Yanling Dao in general.
The correlation is as follows
As for the handle, the handle of Yanling Dao is almost straight, which is normal in The Lancet. It was not until the end of 18 that some downward bends began to appear, and it became popular in the late Qing Dynasty.