SERVICE CHARGES 



199 



From this table and the estimated outputs in the several 

 classes, a rough idea of the required number of meters of various 

 sizes may be made. 



The total number of meters in 33 completely metered sys- 

 tems * may also be of service in making the estimate. 



511,240 



IOO. OOO 



The service charges selected may then be applied to the 

 estimates and the total amount to be probably realized from 

 service charges may be ascertained. 



When the calculation has gone thus far, the rest follows the 

 method given in Chapter XVI. The only difference is that it 

 rests on estimates instead of upon ascertained facts, and when 

 it is completed an addition of the amount allowed as a margin 

 of safety must be made. 



Example. It is desired to make an estimate of the necessary 

 data for a city with a population of 45,000 having 8000 services 

 * Jour. N.E.W.W. Assn., Vol. XXX, p. 460, 1916. 



