Something strange with iTunes Connect sales numbers

[johnqh]

I saw something strange with my daily sales reports.

In iTunes Connect, in Sales and Trends, under "Top Markets". I will use Taiwan as one example. This is the data for the last week.
Date Units Changes
11/28/10 24 -16
11/27/10 19 1
11/26/10 24 -20
11/25/10 17 -29
11/24/10 34 20
11/23/10 22 -26
11/22/10 22 -6
11/21/10 40 6

You can see, the number of units for yesterday plus the number of changes today does not match the units today. There is a close to 40% difference for everyday for the last week or so, sometimes higher, sometimes lower.

What is causing this?

[JasonR]

The changes listed are the changes from the previous week. So the -16 on 11/28 means 16 fewer sales than on 11/21.

They do this because sales vary by day of the week. Games tend to sell more on the weekend. My app for education professionals sells more in the middle of the week. So comparing last week is a better indication of sales trend than day by day.