'Plumbline' in the Bible

Thus hath He shewed me, and lo, the Lord is standing by a wall made according to a plumb-line, and in His hand a plumb-line;

and Jehovah saith unto me, 'What art thou seeing, Amos?' And I say, 'A plumb-line;' and the Lord saith: 'Lo, I am setting a plumb-line in the midst of My people Israel, I do not add any more to pass over to it.