A voltmeter with a selector knob to select one of several voltage scales is called a _____ voltmeter.

A voltmeter with a selector knob to choose from multiple voltage scales is referred to as a multi-range voltmeter. This design allows the user to measure voltage across various ranges, providing flexibility and adaptability depending on the specific voltage level being tested.

The selector knob enables seamless adjustment between different scales, ensuring accurate readings no matter how high or low the voltage. This feature is particularly useful in varied testing environments, where the voltage of the circuit can change significantly.

For instance, in scenarios where a technician is diagnosing circuits with both low and high voltage, a multi-range voltmeter allows for efficiency and prevents the need for multiple separate devices. This is critical in ensuring precise measurements without the risk of exceeding the voltmeter's limits, which could lead to incorrect readings or damage to the instrument.

A single-range voltmeter would only measure one specific range of voltage, thus lacking the versatility that a multi-range voltmeter provides. Digital and analog voltmeters describe different display technologies rather than their range capabilities.