Comprehensive and Detailed Explanation From Exact Extract:

The requirement is:

Compute total sales per customer, not per transaction.

Then compute the average of those customer totals, grouped by region.

Tableau documentation states that FIXED LOD expressions are used to calculate values at a specific level of granularity regardless of the view.

To solve the business need:

Step 1:

Calculate total customer sales for each Customer ID within each Region:

{ FIXED [Customer ID], [Region] : SUM([Sales Amount]) }

This produces one number per customer per region.

Step 2:

Compute the average of those totals:

AVG( { FIXED [Customer ID], [Region] : SUM([Sales Amount]) } )

This yields:

Average total customer sales by region

This is exactly option C.

Why the other options are incorrect:

A. EXCLUDE Region: Would combine regions and incorrectly calculate overall totals.

B. FIXED Region: AVG(Sales Amount): Computes average of line-level sales, not customer totals.

D. FIXED Customer ID + Region: AVG(Sales Amount): Averages individual transactions, not customer totals.

Only option C matches the required two-step logic.

LOD Expressions: FIXED for computing customer-level aggregates.

Nested LOD usage for first calculating customer totals, then averaging them at a higher level.

Tableau guidance: SUM inside FIXED for per-customer totals, AVG outside for averaging customers.