Cutter

I read about Cutter last week. I thought he just spelt out the principles of a library catalogue, ie. that a catalogue's function was to 1. help the user locate a book by author, title and subject 2. show what resources the library has by a designated author and subject in a given literature 3. to help the user find a book in a designated edition (and character actually, but I am not sure what that means.) All that was fine -I understood that, but what I didn't realise (until going online today and doing'Let's Do Dewey') was that there actually are still Cutter numbers used in libraries. If I have understood it correctly Cutter numbers are used when you have more than one book by the same author, so that each book in the library has its own unique number. (Mind you, it involves letters too!) If this is the case how come I have never noticed a book in any library with Cutter numbers? Next time I go to the National Library I will go looking for Cutter numbers!