An oscilloscope probe is a device used to connect a signal source, often a test point in a circuit, to an oscilloscope; a physical connection making the electrical connection. Depending on the signal source and the measurement to make, a probe can be as simple as a wire (e.g. a passive probe) or as sophisticated as an active differential probe, which includes an amplifier to keep the probe input capacitance very low to minimize the influence of the probe on the signal to measure.