Step 1: Set up the view

1. Drag [Customer Name] to the Rows shelf
2. Drag [Sales] to Text on the Marks card
3. Right-click [Sales] on the Marks card and select Quick Table Calculation > Percent of Total
4. Right-click [Sales] on the Marks card and select Compute Using > Table (down)
5. Select Analysis > Create Calculated Field
6. In the Calculated Field dialog box that opens, do the following, and then click OK:
   • Name the calculated field. In this example, the calculated field is named "Rank of Sales"
   • In the formula field, create a calculation similar to the following:
     RANK(SUM([Sales]))
7. Drag [Rank of Sales] to the Filters shelf
8. In the Filter dialog, select 1 to 10 for the range and click OK.

Step 2: Create the new calculation

1. Create a new calculation and drag [Sales] from the Marks card into the calculation editor. Tableau Desktop will automatically write out the formula for percent of total sales, which will look like:
   
   SUM([Sales]) / TOTAL(SUM([Sales]))
    
2. Wrap each instance of SUM([Sales]) with an IF statement that will filter to ranks lower than 10. The final calculation may look like:
   
   IF [Rank of Sales] <= 10
THEN SUM([Sales])
END
/
WINDOW_SUM(IF [Rank of Sales] <= 10
THEN SUM([Sales])
END)
   
   
   Note: It is also necessary to replace the table calculation TOTAL() with WINDOW_SUM(), as TOTAL will only work with aggregations and not with more complex expressions.
    
3. Replace [Sales] with the new calculation