The Pythagorean Theorem is used to determine the side or hypotenuse of a right triangle (a squared + b squared = c squared). It is used when laying out excavation units. The unit is set up with three people and three measuring tapes. Measuring out 2 meters along two directions and then 2.83 meters diagonally across the triangle will produce a perfect right angle. Do it again on the other side and you have a perfect 2 meter x 2 meter unit.