'Plumbline' in the Bible

Thus he showed me: and, behold, the Lord stood beside a wall made by a plumb-line, with a plumb-line in his hand.

And Jehovah said unto me, Amos, what seest thou? And I said, A plumb-line. Then said the Lord, Behold, I will set a plumb-line in the midst of my people Israel; I will not again pass by them any more;