Which type of measurement device shows fluctuations in voltage over time?

The type of measurement device that shows fluctuations in voltage over time is the oscilloscope. An oscilloscope is specifically designed to visualize electrical signals as waveforms, allowing users to view changes in voltage levels over time on a screen. This characteristic is essential for analyzing the behavior of signals in various applications, such as electronics troubleshooting, communication system analysis, and more.

While a voltmeter measures the voltage at a specific moment, it does not provide a time-dependent view of voltage fluctuations. Recording meters can log measurements but are not primarily focused on displaying real-time fluctuations in the same detailed manner as oscilloscopes. Clamp meters are used to measure current flowing through a conductor and do not typically display voltage changes. Hence, the oscilloscope is the best-fit device for observing voltage variations over time.