To measure the difference in elevation between poles, surveyors used an optical level—a telescope on a level base—placed halfway between the poles.

为了测量两极之间的高程差，测量员在两极中间的一个水平基座上使用了光学水准望远镜。

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These are coastal cities, all, thus subject to inundation from the sea or slow draining rivers due to scarce difference in sea level elevation, all signs of sinking.

这些全都是沿海城市，因此会由于海拔的稍稍变化而遭受到来自于海洋的洪水和河流排水缓慢，这都是下沉的迹象。

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