Improvement of the Standard Test Method for Effective Series Resistance (ESR) and Capacitance of Ultra High-Q Capacitors at High Frequencies Francis Rodes and Xavier Hochart U ltra high-Q ceramic chip capacitors exhibit quality factors (Q) higher than 1000. The Resonant Coaxial-Line, manufactured by Boonton [1], has enough resolution for measuring such High-Q factors. As a result, in 1982, the resonant coaxial-line method was standardized by the American Society for Testing and Materials (ASTM) that issued the: " Standard Test Method for Effective Series Resistance (ESR) and Capacitance of Multilayer Ceramic Capacitors at High Frequencies " [2]. Applying this method, we found an error that concerns the measurement of a capacitor serially