What plumb-line? What does it do?
It measures uprightness.
The only time a plumb-line isn’t straight is when the plumb bob, the weight at the bottom of the string, is not where it naturally should be because some force has moved the plumb bob off its center. If we decide to build something (organizations, careers, families, anything) when the plumb bob is out of place, the structure will be misaligned and the and unbalanced, and probably fall.
The simple carpenter's tool represents the idea that to be re-centered we must first understand what upright truly is. Upright never varies. Upright doesn't swing. We should align ourselves, and what we are building, to what is upright.
If we want to get centered, we have to look up, to the top of the plumb-line. That will tell us where we should be.
Amos 7:7