Norton's theorem states that a linear two-terminal circuit can be replaced by an equivalent circuit consisting of a current source in parallel with a resistor. The current source value is equal to the short-circuit current through the terminals and the resistor value is equal to the input or equivalent resistance measured across the terminals. To find the Norton equivalent circuit, the Thevenin resistance is first calculated, then the circuit is shorted to find the short-circuit current value. These two values make up the Norton equivalent circuit with the current source in parallel with the equivalent resistance.