A method of calibrating an inertial unit having an inertial core with vibratory axisymmetric gyros, the method includes the steps of starting from a first position, causing the inertial core to pivot towards a second position about a pivot axis that is different from the sensing axes of the gyros and from a trisector thereof, while taking measurements of an angular orientation of the vibration of each gyro, the angular orientation being left free during pivoting; returning the inertial core to the first position; adjusting the angular orientation of the vibration of each gyro to a value corresponding to the second position; causing the inertial core to pivot towards the second position while once more taking measurements of the angular orientation of each gyro; and calibrating the inertial core as a function of the measurements taken.