If the background current is the opposite polarity, these unwanted currents could current reading.

这就是说,电流的极性和所加电压的极性相反, 于是计算出的电阻将为负值.

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During a reversal, the main field weakens, almost vanishes, then reappears with opposite polarity.

在逆转期间, 主磁场减弱, 几乎为零, 然后以相反的磁极重新出现.

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