Excessive vibration in rotating machinery can substantially reduce the life of shaft bearings.

The process of reducing the out-of-balance forces that cause vibration in rotating machinery is called "Balancing". The unbalance is caused by an effective displacement of the mass centre line from the true axis caused by some mass eccentricity in the unit.

To overcome this problem, Dynamic Balance must be performed. The balancing machine will have both sets of bearing pedestals connected to sensors and the unbalance at the two planes can be independently identified and, thus, corrected.

By the use of electronics and computer control, the actual correction planes can be at any convenient position along the length of the unit relative to the running bearings and, in the case of very long units, more than two planes can be considered.