Why is the edition indicator useful for searching?
From edition to edition, new entries appear in the IPC because there are new technologies for which the coverage was not sufficient in the previous edition. Frequently an existing “classification tree” was modified, because its original design did not fit the needs of the patent classifiers. Often it was transferred to a new place where a new, different classification tree, was elaborated. The consequence of this is that if you found an IPC entry, you should check when it entered into the IPC. If it existed since the beginning, most probably you can initiate a reliable search with that. However, if you have an edition indicator, e.g., [5], this means that the entry entered into the IPC in the 5 th edition. You have to check where technical subject of your interest was classified in the earlier editions. To do this checking, use the Revision Concordance Lists. If you used that symbol without any additional checking, you can automatically limit the scope of the search by limiting the tim
