Page:Graphic methods for presenting facts (1914).djvu/167

 *vidual attending a large exhibition. If the scale were given, however, it would be plotted on the basis of actual horse-power rather than on percentage, for the top curve here represents the total quantity. Percentage scales cannot well be used in diagrams of component parts if a fluctuating curve line instead of a horizontal line representing 100 per cent is given at the top. The reader may, however, get a fair idea of the percentages if he roughly calculates the height of the areas in question on any vertical line of the co-ordinate ruling and then, using that vertical line as a measuring rod, estimates the height of the areas as a percentage of the total height of the chart.

In Fig. 133 the straight line at the top of the chart does not have any significance, as it is due only to the co-ordinate ruling which serves as a background to the chart itself. The important part of the chart ends at the top of the shaded area. We may consider the top of the whole shaded area as a curve and read the values accordingly from the scales on the right- and left-hand sides. In fact, any curve on the whole chart may be considered as a sub-total, which includes all of those components or factors shown as separate areas beneath that curve. Thus the "Total Shop Cost" includes all those components shown below the "Total Shop Cost" curve.

Adapted from Factory

Fig. 133. Factors Entering into the Total Costs and Estimated Value of the Product of a Manufacturing Plant

The various elements entering into total shop cost are plotted, each built up on the areas below. The "Estimated Valuation" is based upon market prices for the finished goods. Vertical distances between the "Total Cost" curve and the "Estimated Valuation" curve show the estimated profit. Note the use of dimension lines in combination with the scales