30 GRAPHICAL COMPARISON OF METER RATES 



The sliding scale in the ordinary form gives a more gradual 

 drop in the lines at the points of change, as at Atlanta, Ga. ; 

 Belmont, Mass., Hartford, Conn., etc., Figs. 3, 4 and 8. 



The effect of the service charge is to give a broad, sweeping 

 curve at the left of the sheet for the lower rates, as at Madison, 

 Wis., Fig. 2. This resembles somewhat in its general form 

 that produced by a minimum rate, but the change is gradual 

 and is represented by a curved line instead of by the two 

 straight lines with an angle which results from the use of a 

 minimum. 



In order to plot a rate schedule, a list of quantities in thou- 

 sands of gallons per annum, ranging from the smallest to the 

 largest, is taken, and the annual payment for each is computed. 

 In doing this, if cubic feet are used and if other periods than 

 the year serve as a basis for the rate schedule, the corresponding 

 quantities in the units of the schedule are found before applying 

 the rates. 



Sometimes a discount for cash payment is allowed, and where 

 this is done, for the purpose of plotting it may be assumed that 

 nine-tenths of the discount is to be deducted on the supposition 

 that on an average nine-tenths of the consumers will avail 

 themselves of it. 



The annual bills for the several quantities of water divided 

 by the respective quantities show the average prices per 1000 

 gallons paid by a consumer drawing those quantities of water in 

 the course of a year, and these average prices are then plotted 

 against the corresponding quantities. 



When there is a service charge depending upon the size of 

 the meter, the rate for any given quantity will depend somewhat 

 upon the size of meter through which that quantity is drawn, 

 and to obtain results that are of value for comparison it is neces- 

 sary to make assumptions as to the sizes of meters that will be 

 used in connection with the different quantities. 



There is no fixed rule governing this. ID. the plot tings here 

 presented it is assumed that meters will be used corresponding 

 approximately with the ordinary average practice of the systems 

 for which returns to the New England Water Works Association, 



