title: Facebook total Reach with insights API
body: <p>On Facebook Insights UI there is a section called "Reach".
  Using page_impressions_unique of Insights API (which is supposed to carry the "Reach" value) I get a value which is 1/3 of the one appearing on UI. It seems they add some other metrics but it's not clear how to get that very same value using page metrics from Insights API.
  <a href="https://developers.facebook.com/docs/graph-api/reference/v2.8/insights" rel="nofollow">https://developers.facebook.com/docs/graph-api/reference/v2.8/insights</a></p>
  
  <p>Does anyone have any clue about it?</p>