You hold the string (which is often coated with brilliantly colored chalk) near the ceiling and let the weight drop to the floor... flick the chalk line against the wall, and you have a mark of what is "true plumb" ... that is, aligned straight up from the center of gravity. Especially in houses that have been around for a while (like mine, built in 1950 or so) the walls may have moved far from "true" plumb. In extreme cases the shift may be so significant that you may decide to avoid wallpaper with vertical patterns because the disparity between what the line of the wall offers and what is "true plumb" is so great that it makes folks dizzy to be in the room.
Plumb must also be determined when brick-layers construct or repair foundations:
By determining plumb you can see which areas of the wall must be adjusted or built up. In extreme cases demolition may be called for. I recall one foundation repair in my own home where the contractor built a new, plumb wall butting up against the old wall...and then once the new wall was in place, the old faulty wall was removed.
The Old Testament reading for this week speaks about the Word of God in terms of a plumb line.
Amos 7:7-9
This is what he showed me: the Lord was standing beside a wall built with a plumb line, with a plumb line in his hand.
And the LORD said to me, "Amos, what do you see?" And I said, "A plumb line." Then the Lord said, "See, I am setting a plumb line in the midst of my people Israel; I will never again pass them by; the high places of Isaac shall be made desolate, and the sanctuaries of Israel shall be laid waste, and I will rise against the house of Jeroboam with the sword."
If the priorities and values that determine your choices are held up to teachings that sprout directly from God (true plumb) is there a disparity? This may be particularly visible when a group (a society, a community, a family, or a congregation) looks at the activities of the last month or year. How have we begun to "lean" one way or another?
How would the Master Craftsman encourage you to make some adjustments so that the flow of all that you do is more clearly in "plumb"?