Last Friday, when we had no internet connection, it was challenging to help students find books on the shelves. One strategy we used was to thumb through the Library of Congress Subject Headings books, which frequently feature call number ranges for various headings. Another strategy is to use the Library of Congress Classification Outline, which allows you to drill down fairly deeply into call number ranges.
Depending on the question, the LC Classification Outline can often be the better tool for locating known items or books on a subject. When a student asked for a copy of a novel by Albert Camus, I knew that his books would be in the Ps somewhere, grouped with other French fiction writers of the 20th century. If I had had the outline handy, I could have identified the call number range quickly (PQ2600-2651). As I learned after checking with Janey and Jin last Friday, you can't find this call number range in the LC Subject Headings books. They were able, though, to look up the range in the multivolume classification schedules that they have in their offices on the 5th floor.
I've saved a copy of the classification outline, which is a condensed version of the more formal classification schedules that catalogers use, in the IS Division folder (look for the folder therein labeled "LC Classification"). If the local network is down, too, as it was on Friday, you won't be able to access this folder, so I have also printed out the outline and will have it available at the reference desk in a three-ring binder.