[en] The functional diagram of a dynamic subtraction device for X-ray-radiometric equipment is presented. Derived are the theoretical expressions for the counting errors of the device depending on the magnitude of loading and the fast response of microcircuits of which it consists. The counting errors which determine the error of the dynamic subtraction device are reduced to the counting errors of the preliminary subtraction performed by a trigger circuit. It is demonstrated that the error of the system increases with the increase of loading. It is assumed that the application of the dynamic subtraction device in X-ray-radiometric equipment for continuous processing of statistical information will essentially decrease the measurement time and simplify the construction of X-ray-radiometric devices