Commonly, the 10 V control voltage is supplied through a resistor. Control is achieved (and current is sunk) by connecting a variable resistor between the control voltage terminal and ground. The two resistors form a voltage divider to produce a control voltage Vc = Vs * (Rc / (Rc + Rs)) where Vc is the returned control voltage, Vs is the source voltage, Rc is the variable control resistance, and Rs is the source resistance. Vs may be greater than 10 V so that a maximum intended value of Rc produces a 10 V maximum control voltage. Rc must be adjusted to a value of 0 ohms (a direct short) to return a 0 V control voltage.