What type of tool is essential for checking voltage levels in a circuit?

A multimeter is an essential tool for checking voltage levels in a circuit because it is designed to measure electrical parameters such as voltage, current, and resistance. When measuring voltage, a multimeter can provide accurate readings of both AC and DC voltage, making it versatile for various applications, including troubleshooting and verifying circuit operation.

The multimeter's ability to switch between different measurement functions allows electricians to diagnose issues effectively, making it a fundamental instrument in electrical troubleshooting and maintenance. The detailed readings can also help determine if a circuit is functioning within the expected voltage levels, or if there may be issues such as shorts or open circuits.

While a clamp meter can check current without direct contact, it does not measure voltage directly. An insulation tester is primarily used for assessing the integrity of insulation within wiring and components rather than directly measuring voltage levels. A ruler, on the other hand, is not used for electrical measurements and has no application in checking voltage. Therefore, the multimeter is the correct and most appropriate choice for this purpose.