Electrical test probes are used to establish a connection between a circuit under test and the measuring instrument. There are several basic types of products. Voltage probes are used to measure voltage. Current probes are used to measure current. Oscilloscope probes have a specified operating bandwidth and, in some cases, built-in switchable attenuators. Differential probes are used to measure differential signals which are referenced to each other instead of ground. By contrast, single-ended test probes are electrical test probes used to measure signals referenced to ground. Logic probes are used to measure logic levels in digital circuits. Semiconductor probes and high-density probes are fine point, spring loaded probes that are usually mounted in a test jig. These electrical test probes are used to test semiconductor interconnects and high-density circuit boards.