The Surcharge assistant has two completely separate components to it.  First is the Invoice calculation feature, which is on the left side of the screen.  The second is the Base Rates calculation, which is on the right side of the screen.  These features are not used in conjunction with each other.  If you are using the Invoice Calculation section then the Base Rates Calculation will not be any use to you and vise versa. 

Let us discuss the two features available to you. The Invoice calculation feature is used to create an actual invoice that you can send to your industry.   It has two sections; Limits and Rates, and Create Surcharges.  The Limits and rates section is used to setup limits and rates on an Industry and parameter level.  This section is much like Monitoring Point limits.  Next is the Create Surcharge section and it is where users can add their surcharge criteria, such as date range and flow. 

The Base Rates calculation creates and exports a surcharge rate that can then be applied to a total volume of water that was used or discharged by the industry.  These rates are often sent to an accounting department where they are used to generate a bill.  If this feature does not make sense to you, most likely you are not using this type of process.

Each of these two sections is described explained below.