'Plumb Line' in the Bible

Thus He showed me [a vision], and behold, the Lord was standing by a vertical wall with a plumb line in His hand [to determine if the wall was straight or if it needed to be destroyed].

The Lord said to me, “Amos, what do you see?” And I said, “A plumb line.” Then the Lord said,“Behold, I am setting a plumb line [as a standard]Among My people Israel [showing the defectiveness of the nation, requiring judgment].I shall not spare them any longer. [The door of mercy is shut.]