Voltmeter Multiplier Formula Calculation

The resistance R_S to be connected in series with a voltmeter of full scale voltage V_V and full scale current drain I_V to increase the full scale voltage to V is:

R_S = (V - V_V) / I_V

The power P dissipated by the resistance R_S with voltage drop (V - V_V) carrying current I_V is:

P = (V - V_V)² / R_S = (V - V_V)I_V = I_V²R_S