A duty-cycle modulated bit signalling method and circuit, comprising: signaling bits by virtue of a duty-cycle ratio; wherein the duty-cycle ratio is varied dependent upon the transmission rate of the signalling. The apparatus is compact, lightweight, and low-noise. The line-shaped light beam preferably has a long dimension parallel to the container axis, and sufficient length to illuminate at least one rib peak and at least one valley between the rib peaks. A user can selectively adjust the effective length of the scaffold and shoring assemblies by rotating the ring assembly. This can reduce the burden of authentication while ensuring security, so that high productivity is guaranteed.