To measure a voltage higher than the maximum scale of a DC voltmeter, one should use?

Using series resistance is the correct approach when measuring a voltage that exceeds the maximum scale of a DC voltmeter. This method helps to extend the range of the voltmeter, enabling it to handle higher voltages without damage.

When series resistance is added to the measurement circuit, it limits the amount of current flowing through the voltmeter, effectively reducing the voltage drop across the voltmeter itself. Thus, the voltmeter can measure a portion of the higher voltage, allowing readings that would otherwise be out of its range. It's essential to choose the right value of resistance to ensure that the voltmeter can still operate accurately within its specifications.

In contrast, parallel resistance would not help in this scenario, as it could potentially lower the overall resistance of the system, increasing the voltage across the voltmeter and risking damage. Variable resistance can adjust the current in the circuit, but it does not inherently extend the voltage range of the voltmeter. Using a different voltmeter might be a practical solution if one is available that can handle the higher voltage, but it does not directly address the method of modifying the measurement approach with the tools already at hand.