Hi Psygorn, CustomUi and FxGraph are different things, one is a UI mod that adds several buttons on the bottom toolbar and the other is a plug-in command.
For FxGraph unzip it and copy the files into the MoI appdata commands folder, it's in the same location as described in the above link for CustomUI as well.
re:
> Dear PILOU, what is the difference between these two?
>
> 1-http://moi.maxsm.net/files/scripts/FxGraph3D.v.1.1.2016.04.17.zip
> 2-http://moi.maxsm.net/files/scripts/FxGraph.v.1.2e.2016.04.17.zip
They are different - FxGraph plots a function curve (parametric function of one parameter) while FxGraph3D plots a surface (parametric function of 2 parameters) .