Which measurement scale on a DMM is most accurate for testing potential difference under load?

The most accurate measurement scale on a digital multimeter (DMM) for testing potential difference under load is the DC Volts scale. This is because DC voltage measurement is specifically designed to accurately gauge the voltage level of a direct current circuit while it is operational and under load conditions.

When measuring potential difference in a circuit, especially in automotive or mobile electronics applications, it's essential to ensure the meter measures the voltage while the circuit components are functioning. The DC Volts setting allows the meter to account for the behavior of the system's voltage – including slight drops caused by resistance under load – providing a more accurate representation of how much voltage is actually available to the components in real-world conditions.

Other settings, like AC Volts, are used for alternating current circuits, which are not applicable in straight DC systems. The Ohms setting is utilized for measuring resistance rather than voltage, and the Continuity setting checks if a circuit is complete, which does not provide a measurement of potential difference. Therefore, the DC Volts scale is specifically tailored for effectively measuring voltage and ensuring accurate readings in a live circuit.