For an outline of the scheme see Library of Congress Classification Outline . LC call numbers begin with letters of the alphabet. No two books have exactly the same call number.
Numbers used in the following examples are hypothetical.
The first line just needs to be treated alphabetically. E24 Line three is often misunderstood. Therefore, .K79 comes before .K8. M35 Line four is called the Double Cutter number. Sometimes call numbers do not appear horizontally, but vertically.