How to find out the amplitude and duration of a voltage sag from the wavelet coeiffients?

Hi

I hav created a voltage sag signal in matlab simulink and imported the voltage signal to workspace.Using wavemenu toolbox in matlab ,analysed the signal with db4 wavelet and observed the detail and approximation coeiffient waveforms.How can we determine the start and end point of a sag and its magnitude?? I attached the voltag sag signal waveform in wavemenu toolbox