Okay, here goes.

Once you know the "hundreds" of the Dewey Decimal Classification (and to a lesser extent Universal Decimal Classification), you can *usually* find your way around because of built-in mnemonics.

For instance, 970 is the number for United States History. 917 is travel in the United States. 813.54073 would be criticism of United States fiction of the latter half of the 20th century.

In language, 440 is French grammar, etc. 814 is French poetry.

But don't think that this holds thoughout, because 640 is NOT applied French science and technology, but Domestic Engineering -- cookbooks, etc.

But hey! It works, and it's better than saying "shelf nine, under the bust of Cleopatra."