A plumb line is a piece of string with a weight attached to the end that is used to check that something such as a wall is vertical or that it slopes at the correct angle. a piece of string with a small heavy object tied to one end, used for measuring the depth of water, or for checking whether something such as a wall is built exactly upright
A vertical guideline (sometimes called a level line) necessary when hanging wallpaper; a length of string is usually coated with chalk to which a weight is attached; when the string is snapped, the chalk leaves a straight line on the wall A level can also be used to achieve the same results by tracing with a pencil on the correctly positioned level