'Plumb Line' 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.

Yahweh said to me, "Amos, what do you see?" I said, "A plumb line." Then the Lord said, "Behold, I will set a plumb line in the midst of my people Israel. I will not again pass by them any more.