This paper describes a generalization of a method used for precision calibration of a strapdown INS. This method was proposed at the Laboratory of Control and Navigation and at the Department of Applied Mechanics and Control, Lomonosov Moscow State University. The method is practically used in specific applications. The purpose of a strapdown INS calibration is to determine the parameters of instrument errors of inertial sensors: accelerometers and gyros (angular rate sensors) to provide compensation in INS navigation mode. It is assumed that the assembled strapdown INS is located on the platform of a test bench. Test bench performs a set of rotations, the choice of which is part of the calibration task. The main source of data used for calibration are the readings of accelerometers and gyros themselves. Two modifications of the proposed method are described. In the first modification, only data from the accelerometers and gyros are used; in the second modification, the angular data provided by the test bench are also used. The estimation algorithms used are Kalman-type filtering algorithms.