f function
Implementation
double f(double px) {
// role (width * height )=> area ((390*844) / 100)*14 / 3288.8;
// double size = px * 329.16; // default size as 1%
return (((((SetDesignPX().screen.width * SetDesignPX().screen.height) / 100) * px) / 3288.8).round()).toDouble();
}