In a right triangle the two legs meet at the square corner and the hypotenuse is the longest side. The squares on the legs together equal the square on the hypotenuse, a² + b² = c²: four copies of the triangle rearranged inside one big square prove it. The theorem gives the brace length, the distance between two grid points and the diagonal through a box. Its converse checks a corner: if a² + b² = c², the corner is square. The crew braces the model clubhouse walls at the Blueprint Table.