Figures are given of the performance of a current transformer with nickel iron core, having a ratio 2000/1, operating on a burden of 100 volt-amperes at rated current. The ratio is within 3 parts in 10,000 of its nominal value in the frequency range 25 cycles per second to 100 cycles per second at full current to one-tenth of full current.In conjunction with a non-inductive resistance of accurately known value and an electrostatic voltmeter, the transformer may be used for measuring currents up to 2000 amperes with an accuracy of a few parts in 10,000.