English: Inventors: Stansbury, Caroll; Montgomery, G. Franklin. This instrument permits a measurement of alternating current to be made without interrupting or breaking the conductor carrying the current to be measured. The heart of the instrument is a small current transformer with a split core that can be clamped around the current-carrying conductor. A transistor amplifier increases the output current of the transformer to an amplitude sufficient to actuate an indicating meter. On its most sensitive range, the instrument sensitivity is 200 microamperes full scale with an accuracy of plus or minus 5 percent over the frequency range of 50 cycles per second to 100 kilocycles per second. Since its development at the National Bureau of Standards, now the National Institute of Standards and Technology, this instrument, or modifications of its basic transducer, have been copied and manufactured by commercial instrument companies in the United States. (1956)