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 cvu've 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

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

Fig. 235. Relations Between Arc of Action in Inches, Pitch Speed in Fee. 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

GENERAL METHODS

a simple chart. Paper having logarithmic ruling in both directions is the kind most frequently used for mathematical charts. Such paper can be purchased from almost any good store selling engineering supplies. Readers wishing to go further into the preparation of charts of this rather highly specialized character are referred to the excellent work of Mr. John B. Peddle, entitled "The Construction of Graphical Charts", published by the McGraw-Hill Book Company of New York City.

The use of isometric paper for drawing charts representing three dimensions was mentioned for Fig. 167. In Fig. 235 we have another application of this same isometric ruling. Instead of "showing the whole sheet of isometrically ruled paper as a background. Fig. 235 shows only enough of the metric ruling to give the impression of three planes meeting like one corner of a box.