At its most basic, an oscilloscope is an instrument that graphs an electronic signal over time. They’re extremely useful when evaluating electronics—particularly when you’re working with analog signals. Most modern oscilloscopes offer a lot of additional features that help you really dig into those signals, but simple oscilloscope functions can be handled by a small amount of hardware. Most of the cost in that case comes from the display itself, which is why you may want to follow this tutorial to turn a USB sound card into an oscilloscope that can be used with your computer.