To link the data from the Customers tab to Reports, Dashboards and Presentations, on the Customers page, select the report you wish to link (choose from list in left sidebar or create a new one), then use the three dots at the top right to select ‘Use numbers for reports & graphs’. (see screenshot below) 
You will then notice a little globe next to the name of the report indicating that these assumptions are used globally in the system.
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