The rectangular method of diagrammatic presentation is difficult to use where the values of item vary widely. For example, if in the illustration given above the number of units sold of commodity A and B are 20 and 240 respectively, the width of the rectangles would be in the ratio of 5:60 or 1:12. If this ratio, is taken, the diagram would look very unwidely. It is order to overcome this difficulty that squares are used.
The method of drawing a square diagram is very simple. One has to take the square-root of the values of various items that are to be shown in the diagrams and then select a suitable scale to draw the squares.