Can you show a screen shot with your marks pane as well? Including a workbook or data would also help.
i have a field for "user email" that i dragged to detail for the min chart (bottom), which gives me unique count of emails. lets pretend i have no other marks anywhere else, ignoring the colors.
Keep in mind color will be a factor if you use it.
This is an approach without taking color in to account:
I used countd instead to avoid putting users on the detail.
Record = session
Customer = user
First pill: sum(number of records)
Second Pill: calc value countd([Customers Name])
Third Pill: calc value sum([Number of Records])/countd([Customer Name])
Let me know if that's what you're looking for
yes, thank you!