visitor to the page, for instance, might see a list of books that share a similar genre and theme, or they might see a list of current scholarship on the book. This content, moreover, offers interactive possibilities for users signed into their Google account. They can export the bibliographic data and citations in standard formats, write their own reviews, add it to their library to be tagged, organized, and shared with other people. Thus, Google Books collects these more interpretive elements from a range of sources, including the users, third-party sites like Goodreads, and often the book's author and publisher. In fact, to encourage authors to upload their own books, Google has added several functionalities to the website. The authors can allow visitors to download their ebook for free, or they can set their own purchase price. They can change the price back and forth, offering discounts whenever it suits them. Also, if a book's author chooses to add an ISBN, LCCN or OCLC record number, the service will update the book's url to include it. Then, the author can set a specific page as the link's anchor. This option makes their book more easily discoverable. Ngram Viewer The Ngram Viewer is a service connected to Google Books that graphs the frequency of word usage across their book collection. The service is important for historians and linguists as it can provide an inside look into human culture through word use throughout time periods. This program has fallen under criticism because of errors in the metadata used in the program. Content issues and criticism The project has received criticism that its stated aim of preserving orphaned and out-of-print works is at risk due to scanned data having errors and such problems not being solved. Users can report errors in Google scanned books at support.google.com/books/partner/troubleshooter/2983879. Scanning errors The scanning process is subject to errors. For example, some pages may be unreadable, upside down, or in the wrong order. Scholars have even reported crumpled pages, obscuring thumbs and fingers, and smeared or blurry images. On this issue, a declaration from Google at the end of scanned books says: As of 2009, Google stated that they would start using reCAPTCHA to help fix the errors found in Google Book scans. This method would only improve scanned words that are hard to recognize because of the scanning process and cannot solve errors such as turned