A book may be found within the proper subject section yet remain hard to locate should it fall several steps back in the call number sequence. One decimal place, letter, or author mark can separate the object from the position listed in the catalog. Call numbers avoid this difficulty by supplying each item an addressed position on a shelf. In so doing, they bind decisions on subject classification, printed spine labels, catalog records, and physical shelf placement as one retrieval apparatus.
Normally the first part of a call number stands for subject matter. This first part may contain only figures, only letters, or a mixture of the two, depending on the subject classification scheme in use. Related subject matter receives similar beginnings so that it is shelved near similar subject matter. The remaining parts of the call number assist in a tighter subject arrangement by such criteria as subtopics, author, title, volume number, or year of publication. It is necessary to read each of these parts in proper sequence, rather than thinking of them as one contiguous string.
One of the frequent errors in call number reading involves misunderstanding of how a decimal works. For example .35 is a decimal smaller than .4, since .4 is understood as .40. If only the number of digits in the decimal is considered, .4 is smaller than .35, so it would be shelved in the wrong place. When you read a decimal one digit at a time, starting at the decimal point, .35 is clearly smaller than .4. The letters of a call number must be considered in their entirety as well. If two authors have similar names, the first letter is checked. Thus B is a smaller letter than C. When two author marks begin with the same letter, a second letter is examined and the third letter, and so on. The same process is followed for figures in an author mark.
It is essential that shelf order exactly correspond with the call number found in both the catalog and the spine label. When there is a discrepancy between the call number on the spine label, the call number in the catalog, and shelf placement, a quick return can leave the book hidden. The label on the spine could be wrong, the object in the catalog could still contain a superseded call number, or the book could have been returned to the wrong location. A careful shelf-read looks first at the correct sequence of material on a shelf and then checks uncertain items against the record.
To practice, write eight sample call numbers on individual index cards and arrange them from left to right. Try to choose at least two with a similar subject area, more than two different decimals, two similar author marks, and one that has a volume number. Then when your cards are ordered correctly, place one into the wrong location. Find it by carefully comparing the call numbers on the new card with the adjacent cards on the left and on the right. Then repeat the process with the index cards standing up as if they are shelf labels for books on a shelf.
The most important aspect of proper shelving practice does not involve being able to recite a long and unfamiliar string of digits and letters but rather to look at one element at a time. Is the subject correct? Is the decimal correct? Is the call letter for author correct? Is the date, volume or other number correct? Don’t go immediately to the author name or even the title on the spine label. If your library materials are in correct subject order, you have a reliable shelf and will be able to search for almost all material except for items that are nearly correct.