To find out if the installed product is really square or rectangular, both of its diagonals have to be measured – must be equal. If they don't, it means, that we are dealing with a rhombus or a trapezoid. We can quickly check it with two thin slats placed flat against each other. First, measure one diagonal and mark the end of the first strip on the second. When measuring the second diagonal, it is enough to compare only the displacement of this end, to find out if the shape is abnormal.
