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 *iture of one dollar. The placing of these trucks on different levels is somewhat confusing, but it was done in order that one truck would not have to be shown back of another. Note the bars behind each truck, to give the component parts of the total expenditure split into different kinds of charges. This chart is grossly misleading because the point where the race started is not shown. It appears, for instance, that for one dollar expended a five-ton gasoline truck will run about twice as far as a five-ton horse truck. This conclusion is entirely unwarranted, and would not be reached by any reader if the chart had been so drawn that the zero point or starting point for the race had been shown to scale at the left end of the chart.

Courtesy of The Scientific American

Fig. 29. The Distance Different Kinds of Trucks Can Travel for One Dollar Expenditure. The Distance They Have Covered May be Judged from the Mile Posts

The reader is likely to be misled by this illustration, because the zero point where the truck race started is not shown on the chart. Distances must not be judged from the left end of the illustration shown above

The black bars used in Fig. 30 to show contagious diseases indicate an excellent method for differentiating items shown in graphic comparison. In the Boston health-report illustration from which this cut was adapted, the infectious diseases were shown in red. By making most of the bars in outline only, it was possible in Fig. 30 to use solid black to get the contrast obtained in the original report by means of red ink.

It is frequently necessary to show increases and decreases on the same chart so that they may