Waveform appears but is not stable

3.1 Check that the trigger source channel is consistent with the waveform being viewed
3.2 Manually adjust the LEVEL trigger knob to see whether the waveform is stable.
3.3 Use AUTO to adjust the waveform automatically to determine whether the waveform is stable
3.4 Adjust time base, rule out false-wave interference (such as alias displayed waveforms)