It can be seen, for instance, that if a definite weight and length of steel plate Vs inch thick is assumed, the width is absolutely fixed. To obtain a curve like that seen for 5 pounds in Fig. 234, it is necessary only to assume a weight of 5 pounds, then choose separate lengths one by one, and compute the widths which would correspond with the lengths selected to give a weight of 5 pounds. The various figures of width obtained are then plotted as points for the 5-pound curve, and a smooth curve is drawn through all of the points, giving the result seen in the illustration. After one curve has been plotted another weight is assumed in a similar manner, and new computations are made for various lengths on the horizontal scale. Though this method of chart-

GRAPHIC METHODS

ing requires some little labor in making the various computations, it is a very excellent one where the chart must be used for frequent reference. The information from such a chart as seen in Fig. 234 may be read from any portion of the chart, even though the intersection of the length and width lines for the size of the plate under consideration does not fall on one of the curve lines drawn. It can be seen for the example stated in the lower left-hand corner of the chart that the intersection of the vertical and horizontal lines of the independent variables falls halfway between the curve for 20 pounds and the curve for 25 pounds.