An optical system representing the configuration of a tested element disposed therein is provided. The low pass filter has output terminals for connecting a load. A conductor is coupled with the elastic member and extending between the two end portions. The distal end includes a distal opening that is smaller than the proximal opening. The building block may also include an external control bus connected to the processor. The rod member, the pulling member and the elastic plate are connected to one another to guide a positioning member to be assembled into the assembling holes in a balance manner, so that the device for assembling and disassembling a bicycle chain makes the assembly of the chain more convenient and simple.