"United States Patent 5,123,087". USPTO Patent Full-Text and Image Database. patft.uspto.gov. June 16, 1992. Archived from the original on January 18, 2017. Retrieved May 11, 2012.
"United States Patent 5,123,087". USPTO Patent Full-Text and Image Database. patft.uspto.gov. June 16, 1992. Archived from the original on January 18, 2017. Retrieved May 11, 2012.