How the shake meter works

There are two coils connected to the hand of the shake meter, one is connected in series with the additional resistance r in the meter, and the other is connected in series with the resistance r to be measured, and then connected together to the hand-cranked generator. When the generator is cranked, current flows through the two coils at the same time, generating torques in opposite directions on the two coils, and the hand of the meter deflects a certain angle according to the size of the composite torque of the two torques. This deflection angle is determined by the ratio of the two currents. The additional resistance is unchanged, so the current value only depends on the size of the resistance to be measured.