[MSNoise] Question

Hi, Having looked at the MWCS.py program I have encountered a section which has not been explained in the paper titled "MSNoise, a Python Package for Monitoring Seismic Velocity Changes Using Ambient Seismic Noise" and I could not find any justification why this has been done. Within the program, before calculating the cross-spectrum between the current and reference CCFs, the minimum values of each window is subtracted and the result is divided by the maximum value. What is the reason for doing this? In the paper it is just mentioned that the windows are mean-adjusted and tapered. I understand the reason behind detrending, mean adjustment, and the tapering, but not the above-mentioned part of the code. Thank you for your help, Regards, Yoones ______________________________