What data should be drawn up after the current/PD characteristic of a resistor practical?

After the current/PD characteristic of a resistor practical plot a graph of the current against the potential difference. The results should be a straight line passing through zero meaning the current us directly proportional to the potential difference. Although if the directions of the current or potential difference are switched their results will still pass through zero. Hworver, if the temperature of the resistor is not kept constant this experiment will no longer be directly proportional, so it is important to switch the circuit off between readings.