Create a Customer Saved Search:
1. Navigate to Lists > Search > Saved Searches > New.
2. Select Customer.
3. Give a name to the Search.
4. Under the Criteria tab > Standard subtab add two fields:
Transaction Fields… Type is any of Invoice, Cash Sale.
Transaction Fields… Main Line is True.
5. Under the Results tab > Columns subtab add one field :
Transaction Fields… Amount.
Summary Type = Sum.
6. In the main area of the Results tab select Transaction : Amount from the Sort By drop down menu.
7. Under the Available Filters tab add one filter:
Internal ID.
8. Click Save.
Create a Custom Entity Field:
1. Navigate to Customization > Lists, Records, & Fields > Entity Fields > New.
2. In the Label field, enter the label of the field. E.g. Total Sales.
3. Uncheck the Store Value checkbox.
4. Under the Applies To tab.
Check Customer.
5. Under the Display tab.
In the Subtab field, select the tab where the field will be placed or select Main to show it in the customer form main area.
6. Under the Validation & Defaulting tab.
In the Search field, select the Saved Search created before.
7. Click Save.