Open the battery box, install three AAA batteries according the polarity mark in the battery box.
打开电池盖，按电池盒上标识的电池极性装入三节七号电池。
One of these polarity flip-flops, known to have occurred 4.18 million years ago, left its mark in sediments in the CAC.
这种磁极颠倒在418万年前曾发生过一次，CAC地区的沉积物中就留下了这次颠倒发生过的痕迹。
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