The effectiveness and efficiency of any search for relevant documents (Rule 61(1)) depend on the degree of order which is available in, or which can be applied to, the collection of documents to be searched, the order allowing the search division to determine sections of the documentation to be consulted. The basic components for creating order in a collection of documents are words, classification units, indexing codes or bibliographical links between documents by commonly cited documents. The order may have a permanent character, as with indexing words, classification symbols or indexing codes, or it may be created on demand by a search strategy judiciously using the above-mentioned basic components, the outcome of which is a section of the documentation which is likely to contain material pertinent to the invention. The search division for reasons of economy exercises its judgement, based on its knowledge of the technology in question and of the available information retrieval systems, to omit sections of the documentation in which the likelihood of finding any documents relevant to the search is negligible, for example documents falling within a period preceding the time when the area of technology in question began to develop. Similarly, the search division needs only to consult one member of a patent family unless it has good reason to suppose that, in a particular case, there are relevant substantial differences in the content of different members of the same family (see B‑IX, 2.4).