The circuit is below. This is from a quiz from earlier this semester. The equivalent circuit for the meter reduces to the D'Arsonval movement in parallel with a resistor who's value is R/2. I know that no matter what current you want to measure, R must be greater than or equal to 18Ω so that the movement will read 90% of the current or better. The equivalent resistance of the meter will never be higher than 1Ω and will not affect the current i0 by more than approximately 1.13%. I was told I was wrong and received only 55/100 on this quiz. I would like some feedback if anyone has the time or the inclination.