Describe the current/PD characteristic of a resistor practical

In the PD characteristic of a resistor practical there is a battery connected to a resistor in series with an ammeter and a variable resistor, and a voltmeter is in parallel across the resistor. Firstly, use the voltmeter to read the potential difference across the resistor then use the ammeter to read the current through the resistor and record these values in a table. Then adjust the variable resistor and record the new readings on the voltmeter and ammeter, do this several times to get a range of readings. Now switch the director of the battery so the direction of the potential difference is reversed and both the voltmeter and ammeter have negative values. Continue to take several readings of the potential difference and current.