Zero-resistance ammeters (ZRAs) are often used to measure coupling currents. The ZRAs may have a resistance of 50 kohm when they are used to measure currents near 1 nA, so calling them ZRA is only an appropriate when the measured current is high, but not appropriate when the current is low. The term often causes a wrong perception that ZRAs have zero resistance. In fact, the only criterion to determine whether an ammeter can be effectively used to measure the coupling currents is how its voltage is close to zero. Therefore, such ammeters have been called zero-voltage ammeters (ZVAs). (c) The Author(s) 2017. Published by ECS. All rights reserved.