Ok then, the potential divider sounds good. It allows for a variable resistor for calibrating too although i would like to do most of that on the PC.

The outputs im using will output AC and DC Ripple. There will be times when a capacitor is connected to the DC side but not always. I read somewhere that the V and A should be sampled at a higher frequency than what they are measuring. It suggested 400 samples per second. Here in the UK the AC is 50Hz so if i take the highest reading from each set of 400 samples and ignore the rest then i should get the values i need.

About rectifying the AC. Correct me if im wrong but im pretty sure i should rectify it *after* the potential divider then deal with it in the same way as the DC Ripple.

Im not sure i understand the resistor part. I see how you got the 3rd formula from the first 2 but i dont know about the rest. For a start, what is E? A search on google said "E is the e.m.f. of the power supply (the theoretical maximum voltage across the terminals when no current is flowing)". That doesnt really make any sense to me.

0.1W seems a little small for something thats dealing with 1A at 50V but i see that if theres hardly any resistance then it shouldnt matter so much. I might understand this better when i understand what E is

What "bunch of fudge factor" would you recommend for that example?