Bandwidth is the basic index of the oscilloscope. It is the same as the definition of the bandwidth of the amplifier. It is the so-called -3dB point, that is, the frequency point when the sine wave is added to the input of the oscilloscope and the amplitude attenuates to 70.7% of the actual amplitude is called the bandwidth. That is to say, using a 100MHz bandwidth oscilloscope to measure a 1V, 100MHz sine wave, the amplitude obtained is only 0.707V. This is only the case for sine waves. Therefore, when we choose an oscilloscope, in order to achieve a certain measurement accuracy, we should choose a bandwidth that is 5 times the highest frequency of the signal.