Which device is primarily used to measure resistance in a circuit?

A multimeter is a versatile instrument primarily used to measure various electrical properties, including resistance. When measuring resistance, a multimeter applies a small voltage across the component and measures the current flowing through it. Using Ohm's law (V = IR), it can then calculate the resistance based on the voltage and current readings.

In contrast, an oscilloscope is designed for visualizing voltage waveforms over time, offering insights into the behavior of signals rather than measuring resistance directly. A galvanometer measures small currents and would not be suited for resistance measurements in typical circuit analysis. An insulation tester, while it measures resistance, is specifically used to check the insulation integrity of electrical wires and devices rather than for general circuit resistance measurements.

Thus, a multimeter is the most appropriate device for measuring resistance in a circuit due to its broad functionality and ease of use in various electrical measurements.