Re: Resistor calculation
please specify the output current and what you want to do with the output, you also say that the input voltage is 0..400 , if you use a resistive divider(2 resistors in series) you will always have a steady input/output division ratio (2/1 3/1 10/1 etc).
You will also have a voltage drop of 320v , if you multiply this with the current you need you get the watts but even with 10ma you will have 3 watts.
You probably need some kind of active circuit.
Alex