What is the primary use of the 250 scale when measuring voltage?

The primary use of the 250 scale for measuring voltage is specifically designed for measuring unknown DC voltage. This scale allows for accurate readings within a certain range, making it particularly useful when the voltage level is not predetermined. The 250 scale is tailored to handle the characteristics of DC voltage, ensuring precision in measurement.

When working with unknown voltages, especially in circuitry, it's essential to have a reliable method of measurement that the 250 scale provides. It establishes a reference point and makes it easier to read and assess the voltage accurately, which is critical for proper circuit function and troubleshooting.

In contrast, other options focus on different aspects of electrical measurement. For instance, measuring currents typically requires a different unit of measurement or scale entirely. High AC voltage measurements involve specialized scales designed for alternating current characteristics, while calibration of the meter pertains to ensuring the device's measurements accurately reflect actual conditions, which is a different function than voltage measurement itself.