Abstract: An apparatus in which a sequence of modules, the sequence including an arbitrary number of modules, can be attached to a base. Each module has an identity. The base initiates an identification sequence, and each module provides its identity. In some embodiments, each module identifies itself in turn, until the end of the sequence is reached. In other embodiments, each module provides its identity substantially simultaneously, and then the identities, in order, are transferred to the base. In this way the number of modules, and the order of the modules in the sequence, can be recognized. The apparatus could be used, for example, as a toy.