How to calculate the contribution of controls and median manually?

I ran the code and by using waterfall graph, I can get the contribution of medias. I am wondering how I can manually find these values with codes (not the predefined function in Google Meridian).
Also, given the leanred parameters for the controls, how is possible to manually calculate the contribution of controls?

The issue names the waterfall graph, predefined Meridian functions, and learned control parameters, but no files or tests. Start by locating the existing waterfall contribution implementation and tracing how it derives media values and control contributions. Done means documenting reproducible manual calculations for both media and controls, including how median values are obtained.

Written by the indexing model from the issue text.