28 GRAPHICAL COMPARISON OF METER RATES 



number of different meter rates in direct comparison with each 

 other on a single sheet. More simply, two sheets may be super- 

 imposed upon each other, when the comparison of the two rates 

 represented will be at once apparent. 



The primary line plotted and the one to which most impor- 

 tance is attached is the average price per 1000 gallons. This is 

 the most useful basis of comparison. 



Another less generally useful but often helpful basis is to 

 compare the annual bills. These may be plotted on the same 

 paper, three lines being normally used, the first one running 

 from the beginning of the scale up to services having bills of 

 $50 per annum, the second line showing bills running from $50 

 to $500 per annum, and the third line showing bills running from 

 $500 to $5000 per annum. From these diagrams the quantities 

 of water that can be purchased for various sums of money per 

 annum can be at once ascertained. 



On this form of diagram the simplest plotting is, of course, the 

 uniform rate. An unlimited uniform rate would be represented 

 by a horizontal straight line going entirely across the diagram. 

 If a minimum is used, the horizontal line will stop at the point 

 corresponding to the greatest quantity of water that can be 

 drawn under it and a diagonal line will go from that point 

 upward to the left, giving rates for smaller quantities that are 

 proportional to the reciprocals of those quantities. The rate 

 sheet of Chelsea, Mass., Fig. 6, page 43, is mentioned as a 

 plotting of this kind. 



With the sliding scale the line is higher at the left for the 

 small quantities and gradually falls toward the right for the larger 

 quantities. If the amount of slide is comparatively small, the 

 drop is not very great, as for instance at Winnipeg and at 

 Oak Park, Figs. 1 1 and 16. The drop may come all at one point 

 or be distributed at a number of points, according to the num- 

 ber of steps in the slide. 



The jump scale gives a line with steps as at Harrisburg, Pa., 

 and Oak Park, 111., Figs. 7 and 16. The modified jump schedule 

 porduces less abrupt changes, as shown by examples at 

 Syracuse, N, Y., and Winnipeg, Can., Figs. 10 and n. 



