Electric system voltmeter circuit

The voltmeter is composed of a fixed coil and a moving coil in the measuring mechanism connected in series and equipped with a certain additional resistance. Nl is fixed coil,
N2 is moving coil, R. , Rz is the additional resistance, U1 and U2 are the voltage limits.
    When the additional resistance R is greater than the inductive reactance of the fixed coil and the moving coil,
the effective value of the current in the fixed coil and the moving coil is
    I=U/R
in the formula U-the effective value of the measured voltage;
    Ni-the additional resistance of the voltmeter .
    The deflection angle of the voltmeter is calculated by the formula a=KU/Rz.
    It can be seen that the deflection angle of the pointer is proportional to the square of the effective value of the measured voltage,
so the scale graduation is also uneven. Similarly, the electromechanical voltmeter can measure DC voltage and the effective value of sinusoidal AC voltage and non-sinusoidal AC voltage
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