The software peeps at our company make these neat reports for our business peeps. For example, we might have a report called "Sales by Day":

Sales by Day Report

Day	Sales
Monday	$100.00
Tuesday	$200.00
Wednesday	$450.00
Thursday	$250.00
Friday	$120.00

Another report may be Sales by Store (for all time):

Sales by Store Report

Store	Sales
San Diego	$10,000.00
Boston	$30,000.00
Salt Lake City	$25,000.00
Gotham	$45,000.00

Now, if we wanted to show a breakdown per store mixed with per day, as in the following example, which title would be correct, and why?

Sales by Store by Day Report or Sales by Day by Store Report

San Diego

Day	Sales
Monday	$20.00
Tuesday	$25.00

Boston

Day	Sales
Monday	$35.00
Tuesday	$45.00

....

Solution 1:

I would replace one of your by with per:

Sales by Day per Store

Sales per Day by Store

In this context by and per are effectively synonymous, so you can use either variant. However, for consistency's sake you should probably use per consistently in one half of the formula or the other, so that you always say (for example) Sales Per Day, whether or not the store breakdown is given.

Solution 2:

First, offset the "levels" with commas or parentheses:

Sales by Store (by Day)

or

Sales by Store, by Day

If you are asking about the order, I think the correct order would be innermost to outermost grouping, but I cannot cite any authority for that, just experience.

Sales by Day, by Store

Solution 3:

Looking at your two single-level examples (Sales by Day and Sales by Store), the Sales (numbers) appear on the right side, and the ordering qualifier appears to the left. So for consistency, I think I would continue that trend.

In your final example, sales are furthest to the right, then days, then stores - so I would title the report Sales by Day, by Store.

In all fairness, however, I could probably convince myself the other way too. As long as the labels of the qualifiers are clear, I don't think the title will lead to any confusion.

(edited to take @JeffSahol's excellent suggestion of offsetting by commas)

Solution 4:

Since the way you've grouped the data

It should say

Sales by Store by Day

or even better

Daily Sales by Store

Hope that helps!!!