Why may "Page Reach" be different in Databox vs Facebook?

Facebook stores daily values for "Page Reach" in its API. This means that each day, the total number of unique people who saw any of your Page posts is synced with Databox. 

In order to allow Databox users to report on "Page Reach" for Date Ranges longer than "Today" and "Yesterday," we must aggregate these unique, daily values. 

For example, to report on "Page Reach" for the Date Range "Month to Date," we add together all daily "Page Reach" values from the month. This value in Databox may be slightly higher than the "Page Reach" value you see in Facebook because unique values were added together. 

This is because a user may see your Page post on the 1st of the month, and then again on the 8th of the month. In Databox, we are counting that twice for the monthly "Page Reach" value (one on the 1st and one on the 8th). In Facebook, they are only counting that once for the monthly "Page Reach" value, since they can identify that the user who viewed your Page post on the 1st is the same as the user who viewed your Page post on the 8th. 

If the same person views your Page post multiple times in the same day, they will only be counted once in Facebook and in Databox.