In December 2010 Google introduced the Google Books Ngram Viewer, a phrase-usage graphing tool developed by Jon Orwant and Will Brockman of Google that charts the yearly count of selected n-grams (contiguous sequences of n items from a given sequence of text or speech) in the Google Ngram word-search database. The words or phrases (or ngrams) are matched by case-sensitive spelling, comparing exact uppercase letters, and plotted on the graph if found in 40 or more books during each year of the requested year-range.
"The word-search database was created by Google Labs, based originally on 5.2 million books, published between 1500 and 2008, containing 500 billion words in American English, British English, French, German, Spanish, Russian, or Chinese. Italian words are counted by their use in other languages. A user of the Ngram tool has the option to select among the source languages for the word-search operations" (Wikipedia article on Google Ngram viewer, accessed 12-08-2013).