Double-checking for square Before cutting, nailing, or pouring concrete, it’s wise to double-check the layout using a different rule of geometry: Diagonals of a rectangle are the same length.

It has four right angles (90°). The opposite sides are parallel. The diagonals bisect each other. The exterior angles of a rectangle are each 90°. A parallelogram has two pairs of equal sides.

is primarily interested in the geometric symmetry of his model or subject. He established a central vertical and the subject is then drawn between balancing diagonals and their reciprocals.