Hunter GSP9720JLR Operation Instructions Manual page 142

During Forcematching, the first harmonic vibration of the tire is matched opposite of
the first harmonic vibration of the rim to decrease the first harmonic vibration of the
assembly. This reduces the vibration felt inside of the vehicle.
A vibration that occurs twice for every revolution is defined as a second harmonic
vibration. Because there are two vibrations per revolution, the second harmonic
vibration occurs at twice the frequency of a first harmonic vibration:
Multiple harmonic vibrations may also occur. For instance, the third order vibration
causes a three times per revolution vibration:
Multiple harmonic vibrations may occur at any harmonic factor, dependant only upon
the number of vibration components in each revolution.
134 x Theory of Operation
GSP9720JLR Wheel Balancer Operation Instructions