After the bearing is installed in the main engine, if the radial runout of the main shaft is measured, it can be found that the measured value of each rotation has a certain change; During continuous measurement, it can be found that after a certain number of revolutions, this change will approximately repeat. The number to measure the degree of this change is the circle rotation accuracy. The number of revolutions required for the change to approximately repeat represents the "quasi period" of the circle rotation accuracy. A large magnitude change within the quasi period means a poor circle rotation accuracy.