1. Day, J. L., and La Pinta, C. K. (1973). Int. Conf. Biomed. Electrode Technol., 1st, Stanford, Cal. p. 123.
2. “Results of the First U.S. Manned Orbital Space Flight.”;Johnston,1962
3. Anonymous (1961). EKG Amplifier, Specification Control Drawing No. 45–88726. McDonnell Aircraft Corp., St. Louis, Missouri.