The document discusses balancing of rotating masses. It defines balancing as restoring a rotor with unbalance to a balanced state by adjusting mass distribution about its axis of rotation. It describes four cases of balancing: a single mass with a single mass in the same plane; a single mass with two masses in different planes; different masses in the same plane; and different masses in different planes. It provides details on balancing a single mass with one or two masses in other planes, including the conditions that must be satisfied. Finally, it mentions analytical and graphical methods can be used to determine the balancing mass magnitude and position.