[quote]
Originally posted by bigqueue
[b]
Let me ask why you would want to add any resistance into the circuit when you can use the resistance that exists there already?
(and is required by the laws of FIRST 
)
Please read my post again. We are doing essentially the same thing you are: measuring the voltage drop across an already existing component in the system (negative lead to SC). However in our design the shunt resistance will not change (wire has much better resistance stability than the circuit breaker) as much and so the calibration is much more stable. Also, we don't have to used an expensive differential instrument amplifier and the associated extra wires. The dual channel R-R op-amp from Digikey is only $1.35 and it runs two channels of current sensing. One pot, two resistors and a capacitor make up the rest of the variable-gain amplifier.
I post the hand-sketched circuit diagram.