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A precision resonance method for measuring the dielectric properties of low loss solid materials has been developed in our laboratory. The dielectric sample to be measured is shaped into a cylindrical disk and inserted into a cylindrical cavity resonator oscillating in the T10, mode. Â¿ can be measured from the difference between the axial lengths of the cavity tuned to the same frequency with and without the sample, and tan a can be found from the difference between the Q's of the cavity with and without the sample. By making use of a special marker of a resonance point on an oscilloscope, the measurements accuracy can be improved to yield only 1 per cent error in Â¿ and 3 per cent error in tan a for various low-loss samples. Such materials as polystyrol, polyethylene, teflon, and glass for high-frequency use were tested at 4,000 mc, 9,000 mc and 24,000 mc.