[Line width calculation]

How does Cura calculates the line width, mean it, what is the mathematical function that Cura uses for calculating the amount of extruded material for Wall Flow, Top/Bottom Flow, Infill Flow etc. and/or where can it be found in the GitHub files?

[Underextrusion on outer wall]

Do you still have the old profile? I really want to compare it to the default, because I too have/had that problem.