The Theory Behind Consumption Estimation Using Trends
The following discussion explains how the sample estimation plug-ins use trend data. If you decide to create your own version of one of these plug-ins, you still have to set up trend areas and trend classes as these are required fields on premises and SP types.
The standard estimation plug-ins assume that if a customer historically used, say, twice as much as customers of a similar profile, then the customer should use twice as much in the current period. Therefore, to estimate consumption for any period of time the system needs to know:
A. How much the specific customer used in the previous consumption period.
B. How much the average customer in the customer's trend profile used in the previous consumption period.
C. How much the average customer in the customer's trend profile used in the period being estimated.
Once the above are known, estimated consumption for the specific customer equals (A/B) * C.
Knowing how much the specific customer used in the previous consumption period simply involves looking at the customer's previous readings (or reading, in the case of consumptive meters).
Knowing how much the average customer used requires consumption trend data. Consumption trend information is continuously updated behind-the-scenes using meter reads. A consumption trend is identified by a unique combination of:
• Trend area. Trend areas are used to differentiate consumption trends in different geographic areas. If your service territory doesn't have appreciable differences based on geography, then you will have just one trend area.
• Trend class. Trend classes are used to differentiate consumption trends based on the type of service and the type of property. At a minimum, you would probably have a trend class to differentiate between residential, commercial, and industrial usage.
• Unit of Measure and Time of Use. All consumption in the system is identified using a unit of measure code and, optionally, a time-of-use code.
Fastpath: 
For more information about unit of measure codes, see Setting Up Unit Of Measure Codes . For more information about time-of-use codes, see Setting Up Time-Of-Use Codes . Trend areas, trend classes, and consumption trends are described later in this section.
Note: 
Bottom line. A separate consumption trend is maintained behind-the-scenes for every combination of trend area, trend class, unit of measure and time of use.