- Static balance is balance on a rotating plane, it may not be necessary to measure phase, just a handheld vibration meter is enough. The concept of static here is not standing still. In the past, people did it like this: put the shaft on 2 pillows, which are 2 knife blades, to find the heaviest position. But now let it rotate at a fixed speed, then measure and calculate it.
- Dynamic balance is balance from 2 or more planes of rotation. In terms of calculation theory, we use the influence coefficient matrix.

What is rotor imbalance?
-  Is the vibration of the rotor due to centrifugal force when rotating, the cause is the heterogeneity of materials and shape of the rotor. It can be imagined that the rotor has two extra masses attached at two balanced processing planes. or the rotor's center of gravity is not on its axis of rotation.

What are hard shaft rotors and soft shaft rotors?
- Rigid shaft rotors are rotors that do not deform when changing rotational speed and do not operate at their resonant frequency.
-  Flexible shaft rotors are rotors that deform when changing rotation speed. Or rotors operating near their resonant frequency. With these rotors, when dynamically balancing, it is necessary to rotate them at a high speed close to their working speed