U.S. Patents Granted, Patents Granted, 
                      Logarithmic Plot, pg 106. 
                    Source:
                      
                      The patents used in this chart are, as described 
                      by the U.S. Patent and Trademark Office, “patents 
                      for inventions,” also known as “utility” 
                      patents. The U.S. Patent and Trademark Office, Table of 
                      Annual U.S. Patent Activity, http://www.uspto.gov/web/offices/ac/ido/oeip/taf/h_counts.htm.