The addition of a resistor influences the voltage (V) and the current (I) according to Ohm's Law: V = IR, where R is the resistance of the resistor. In a series circuit, in which resistors are added tail to head along a circuit, the current across each resistor is the same, and the total resistance is the sum of the individual resistances: . In a parallel circuit, in which resistors are aligned in parallel, and the current has multiple pathways available, the current through each resistor is only the same if the resistance of the resistors in parallel are the same. The total resistance in a parallel circuit is the reciprocal of the sum of the individual reciprocal resistances: .