The rule or masonry rule is a strong, thick and long wooden rule or strip, used in masonry, which is used to take distances. It is of variable dimensions, with its faces perfectly straight and flat at right angles and which can be divided according to its length in feet "Foot (unit)") and inches or in decimeters and centimeters.

Slats whose three dimensions are different are called rules, and slats when they have the same board as the edge; Each bricklayer must have at least one rule 2 meters long by 0.10 meters wide and 0.03 meters deep and two rulers of equal length by 0.04 meters square each. Placed the rulers vertically with the plumb line, fastened with iron pegs, a type of hook nail that is nailed to the wall, paired one on each side of the ruler and two at each end, they prevent it from moving and serve to tie to them at equal height the guy rope, which is a hemp twine that is fixed with loops to the pencil or saw markings on the ruler and which thus mark the rows or courses of the bricks and serve as a guide for the bricklayer to place them regularly.

The rules are used to mark the marking on the walls and even the surfaces of the flooring, so that all the pieces or tiles remain on the same plane.