1, for simple harmonic vibration (such as spring oscillator, simple pendulum, etc. ), the amplitude can be calculated by measuring the maximum displacement. The amplitude is equal to the absolute value of the maximum displacement.

2, for periodic fluctuations (such as sine wave, cosine wave, etc. ), the amplitude can be calculated by measuring the height of the peak or trough. The amplitude is equal to the value of the peak (or trough) minus the equilibrium position of the wave (usually zero).

3. For the AC signal in the circuit, the amplitude can be calculated by measuring the maximum value of voltage or current. The amplitude is equal to the absolute value of the maximum value.