$13.$ True or False: Graphical methods in balancing can visually demonstrate the effects of added or removed masses.

$14.$ True or False: Mass distribution has little effect on the vibration characteristics of an engine.

$15.$ True or False: Torsional vibrations in drive shafts are primarily caused by improper alignment.

$16.$ True or False: Balancing a rotor always involves complex mathematical calculations and cannot be done through empirical methods.