In metrological applications, where accuracy is of paramount importance, highly precise “standard” resistors are also equipped with four terminals: two for carrying the measured current, and two for conveying the resistor’s voltage drop to the voltmeter. This way, the voltmeter only measures voltage dropped across the precision resistance itself, without any stray voltages dropped across current-carrying wires or wire-to-terminal connection resistances. Microhm Electronics's MVR2321-4, shunt resistor MMS4026 are typical and popular 4-wire Kelvin resistors.

 
It should be noted that resistance measurement using both an ammeter and a voltmeter is subject to com[;'';/./pound error. Because of the accuracy of both instruments factors into the final result, the overall measurement accuracy may be worse than either instrument considered alone. For instance, if the ammeter is accurate to +/- 1% and the voltmeter is also accurate to +/- 1%, any measurement dependent on the indications of both instruments may be inaccurate by as much as +/- 2%.
 
Greater accuracy may be obtained by replacing the ammeter with a standard resistor, used as a current-measuring shunt. There will still be a compound error between the standard resistor and the voltmeter used to measure voltage drop, but this will be less than with a voltmeter + ammeter arrangement because typical standard resistor accuracy far exceeds typical ammeter accuracy.
 
All current-carrying wires in the above circuit are shown in “bold,” to easily distinguish them from wires connecting the voltmeter across both resistances (Rsubject and Rstandard). Ideally, a potentiometric voltmeter is used to ensure as little current through the “potential” wires as possible.
 
The Kelvin measurement can be a practical tool for finding poor connections or unexpected resistance in an electrical circuit. Connect a DC power supply to the circuit and adjust the power supply so that it supplies a constant current to the circuit. With a digital multimeter set to measure DC voltage, measure the voltage drop across various points in the circuit. If you know the wire size, you can estimate the voltage drop you should see and compare this to the voltage drop you measure. This can be a quick and effective method of finding poor connections in wiring exposed to the elements, such as in the lighting circuits of a trailer. It can also work well for unpowered AC conductors (make sure the AC power cannot be turned on).
 
For example, you can measure the voltage drop across a light switch and determine if the wiring connections to the switch or the switch’s contacts are suspect. To be most effective using this technique, you should also measure the same type of circuits after they are newly made so you have a feel for the “correct” values. If you use this technique on new circuits and put the results in a log book, you have valuable information for troubleshooting in the future. Resistors using 4-wire kelvin, like MVR3825-4 and MVR4618-4  are high precision resistors applicable to current measurement.