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 *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. The weight is accordingly taken as 22-1/2 pounds.

''Data of Guido H. Marx. Courtesy of the Standard Corporation, Philadelphia''

Fig. 235. Relations Between Arc of Action in Inches, Pitch Speed in Feet per Minute, and Breaking Load in Pounds, for Cut Cast-iron Gears of Ten Diametral Pitch

This illustration is drawn on isometric ruling, with the ruling itself seen only as a background so as to give the appearance of a solid model in three dimensions

Though the subject cannot be fully gone into here, it may be suggested for those who care to consider further the general type of charts represented by Fig. 234, that much work may be saved by making such charts on logarithmic paper. This subject has been discussed at greater length in a preceding chapter. There are many classes of data which, when plotted on ordinary squared co-ordinate paper, involve plotting many points to produce curves like those seen in Fig. 234, but for which the same data shown on paper with logarithmic ruling would give straight lines. When the curve lines are straight lines, it is necessary to plot only two points for each curve and then draw a line connecting those two points. This permits a very rapid construction of the chart. A little practice in the making of charts is necessary before one can determine clearly the best method to use so as to produce