What does an oscilloscope primarily measure?

An oscilloscope primarily measures voltage signals over time, allowing users to visualize electrical signals in the form of waveforms. This capability is crucial for analyzing the characteristics of these signals, such as frequency, amplitude, and waveform shape. By providing a graphical representation, an oscilloscope helps technicians determine how a voltage signal changes with time, which is essential for troubleshooting and analyzing electronic circuits.

While it is true that oscilloscopes can also interact with current flow in indirect ways (like using a current probe), their main function is to measure and display voltage levels of signals as they change, thereby enabling a comprehensive analysis of electronic behavior. The capability to measure resistance in a circuit is not within the primary function of an oscilloscope; that would typically be the role of a multimeter. Thus, while other options may touch on related concepts, option C accurately captures the primary purpose of an oscilloscope.