  Modern commercial direct-current current transformers (DCCT) can measure
currents up to the kA range with accuracies better than 1E-5. We discuss here a
DCCT calibration method and its implementation with commercial instruments
typically employed in low resistance calibration laboratories. The primary
current ranges up to 2 kA; in the current range below \SI{100}{\ampere} the
calibration uncertainty is better than 3E-7. An example of calibration of a
high-performance DCCT specified for primary currents measurement up to 900 A is
discussed in detail.
