在理想的情况下，当把电压表连接到一个没有电压的、阻抗比较低的电路时，电压表的读数应当为零。
Ideally, when a voltmeter is connected to a relatively low impedance circuit in which no voltages are present, it should read zero.
与四点同线探针法一样，如果样品电阻和电压表的绝缘电阻（电压表的公共端到地）是同一数量级的，就可能需要使用差分测量。
As with the four-point collinear probe method, a differential measurement may be required if the sample resistance is of the same magnitude as the isolation (meter common to ground) of the voltmeter.
这个相加的电压主要为电源频率的信号，其对于电压表读数的影响决定于电压表的串模抑制能力。
This added voltage is mainly power line frequency and its effect on the voltmeter reading will depend upon the normal-mode rejection capability of the meter.
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