What is the edition indicator?
The edition indicator is presented in square brackets after the entries. If there is no edition indicator after an entry, it means that the symbol is in the IPC since the first edition. An edition indicator [7] means that this entry entered as new into or was substantially modified in the 7th edition. The indicator [4,7] means that the entry appeared as a new one in IPC edition 4 and it was changed in edition 7 (the title of the entry was modified in a way that the scope of the entry was changed). From edition to edition new entries appear in IPC, because there are new technologies the coverage of which is not detailed enough in the current edition. Frequently an existing “classification tree” should be modified, because its original design didn’t fit the needs of the patent classifiers. Frequently it is transferred to a new place where a new, different classification tree, is elaborated. The consequence of this is that if you found an IPC entry, you should check when did it enter into
