In this tutorial, we learn how to build plumb walls. A plumb bob is a weight that you can use to make sure your walls are plumb. This tool is the most accurate tool you can get to plumb up any wall. Your level is only good until it's dropped, this won't be ruined and will always be accurate. When using a plumb bob, you have to get up close and personal to the floor and the ceiling. You will need someone on the floor and someone on the ladder to make sure you get the bob exactly on the line. Then, call it good and have the person mark the spot on the ceiling.