An instrument designed to measure resistance to the direct current (DC) of a circuit conductor. It may consist of a simple unit that detects continuity and shows the results using lighted displays [(e.g., light-emitting diodes (LEDs)], or use a four-terminal technique to measure resistance (e.g., in milliohms) and display the numeric results; it typically includes a DC power supply (e.g., a battery). The device may include visual or audible signals that are activated when the circuit is open and/or the resistance is under a predetermined value. It is used to determine the continuity of conductors and other low resistances such as the contact resistance in electrical receptacles.