The Subject Catalogue on large cards can be used to advantage only with the aid of the Classification or Index. To find what the library has on any given subject, get from the Index the class number of that subject. Under this number in the Subject Catalogue will be found the full titles of the books, with imprints, cross references, and notes. The class number, by which the cards are arranged, is given in the upper left corner and immediately under it is the book number. Any other class number given in the left hand margin refers to another subject of which the book also treats. When the class number at the top is followed by an additional figure in brackets, the subject as given in the printed scheme has been subdivided in arranging the cards. This subdivision will be found on the first card of the catalogue which bears this class number. These figures in brackets determine the arrangement of the titles in the Catalogue, but on the shelves, in the Shelf Catalogue, and in calling for and charging books, they are entirely disregarded. Thus a book numbered 942(7).14 would be in the Catalogue among the 942 cards arranged by the figure in brackets as though it were a decimal, but it would be called for as 942.14, the brackets indicating that the final classing was limited to the Catalogue and was not extended to the shelves. If a fourth figure is added without brackets, the final classing is extended to the shelves as well as to the catalogue, and all the figures must be used in calling for the book. In such cases the added figure is treated as a decimal in the arrangement, though the decimal point is not written.
The last card which bears any class number, gives under that number, followed by the word SEE the call numbers of other books which treat of the same subject, but are classed elsewhere. General cross references are also made in many cases without specifying individual books, as from Commerce as a question of SOCIAL SCIENCE (380) to Commerce as a USEFUL ART, Book-keeping Business Manuals, etc. (650). In such cases there is a card under 380 marked SEE 650, and under 650 there is a card marked SEE 380. From whatever stand-point a subject is approached, the cross references guide at once to the same subject treated in its other relations. These cross references both general and specific are often accompanied by brief notes, characterizing the books to which reference is made.
There will be found at the beginning of many class numbers, a card noting the most reliable books on that subject, and the best of the articles in periodicals, transactions, and collected works with the volume and page where they may be found. It is hoped to give special prominence to these notes for the guidance of readers, and they will be added as rapidly as other duties allow.
Many subjects will have no sub-section cards at the beginning; some will have no reference cards at the end; and some may have no titles given under the number. The scheme provides a place for books on all subjects, whether the library has them or not, so where no titles are given under a class number it shows that the library has as yet no books on that subject.
Articles in periodicals and transactions, separate volumes of sets and collections which are located together, if catalogued are put under their proper subject number, but no book number is given with it. The call number of the book, where they may be found, is always given in the margin preceded by the word IN. In the same way special chapters in books will sometimes be catalogued, e.g. a card marked 338 IN 331-27, would mean that in the 27 books on 331, Capital and Labor, there was a chapter on 338, Production.