1.改装前后电压U=3mA X 100欧=0.3V；2.改装后电流表分支电流仍为3mA，则分支电阻电流为3-0.003=2.997 A；3.分支电阻R=0.3/2.997=0.1001欧
设电阻值为x,流经电阻的电流I(r)=3A-3mA=2.997A,由于是并联,I(r) * x = Rg * 3mA求得 x 约为0.1欧
