Using blueprints of the house, a laser level, several long measuring tapes, and a calculator, the footing contractor determines the location and depth of the wall and post footings. Here you can see one method of laying out and marking the location of footings using hydrated lime or dry mortar mix.

Geometry and algebra are both used every day during the construction of a new house. With three measuring tapes and two people, you can lay out footings that you know are square. Use the wall dimensions in the drawings to create the 2 legs of a right triangle and measure the diagonal distance between the unconnected ends as the third side of the triangle. You do still remember how to use the Pythagorean theory don't you?