Prevent the device from being damped by water or rained. Don't place any container with liquid inside on the cover of device, such as a flower flask.

请勿使机器沾水或被雨淋。请勿将任何盛有液体的容器放在机盖上，例如花瓶。

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Later versions submerged the needle in liquid inside a closed container--these "damped" compasses were more stable, since the liquid kept the needle from swinging and shaking.

FORBES: No. 3 The Compass