No other source could ever equal Bell's personal and detailed description of the steps leading to his remarkable invention. This description is included in Bell's testimony before various courts in the years 1879, 1883 and 1887 when his exclusive patents rights were being questioned by the United States Government. In preparing his defense, Bell provided important insights into the process of his own experimentation leading to the first crude telephone. In his introduction, Charles H. Swan describes Bell's testimony as "... the most detailed and best arranged statement of his telephone work".