1. A method of making a system of representations of printed circuit board sections and comprising the steps of forming at least two printed circuit board (p.c.b.) section representations having portions corresponding to inter-p.c.b. section connections which are to provide interconnections between two circuit portions respectively represented by the representations, arranging each p.c.b. section to correspond to a respective one of a plurality of functional modules comprising apparatus based on the complete circuit and arranging the corresponding inter-p.c.b. section connection portions of each of the representations in predetermined positions such that visually continuous interconnections can be formed between the circuit portions when the representations are caused to provide a visual pattern of the complete circuit represented by the combined representations, at least one of the representations, being of a first functional module, being capable of being substituted by a representation of a second functional module different from the first functional module while still maintaining the visual continuity of the necessary inter-p.c.b. section interconnections with the representations immediately adjoining the substituted representation.