In many foreign products, such as Liebherr, Manitowoc, Terex, Demag, Grove, Kato, Tadano, RIGO, etc. Some designs calculate the length of wire rope by calculating the number of revolutions of winch drum, but it is not difficult to use it reliably and accurately in practical application, and this function is basically abandoned, leaving only the functions of prompting the running direction and roughly prompting the running speed of winch. The upper limit of the hook is basically a chain hammer switch, and the lower limit of the hook is only designed with three wire ropes at the end of the hoist, while others are not designed at all. Crane manufacturers have not adopted the real lower limit of hooks. Even if the lower limit of the hook is designed, in actual work, the crane driver must operate the crane according to the lifting commander, who only visually observes the position of the hook, and can't see or look at the number of the lower limit of the hook. This function seems to have no practical significance.