BD-3197: Clarify audience stats and reachable users

_docs/_user_guide/engagement_tools/campaigns/building_campaigns/targeting_users.md

@@ -63,7 +63,11 @@ For more information and best practices, refer to [Multivariate & A/B Testing][4
 
 ## Audience statistics
 
-Braze provides detailed audience statistics of the targeted channels in the footer.
+Braze provides detailed audience statistics of the targeted channels in the footer. 
+
+For campaigns, select **Calculate Exact Statistics** to determine an accurate number for your reachable users as this will search through every user in your user base. The number of reachable users may decrease if you use a [Global Control Group]({{site.baseurl}}/user_guide/engagement_tools/testing/global_control_group/) or set up message eligibility.
+
+For segments, the larger your user base is, the more likely the **Reachable Users** amount is a rough estimate. For more details, refer to [Calculating exact statistics]({{site.baseurl}}/user_guide/engagement_tools/segments/creating_a_segment#calculating-exact-statistics).
 
 ![][24]
 

_docs/_user_guide/engagement_tools/segments/creating_a_segment.md

@@ -102,6 +102,7 @@ For a user to be listed as reachable through a certain channel, the user must ha
 A single user may belong to different reachable user groups. For example, a user might have both a valid email address and valid Android push token and be opted in to both, but have no associated iOS push token. The gap between the total reachable users and the sum of the different channels are the number of users who qualified for the segment but they are not reachable via those communication channels.
 
 #### Calculating exact statistics
+
 The larger your user base is, the more likely the **Reachable Users** amount is a rough estimate. This allows us to quickly provide you estimates in real-time as you add filters, rather than searching your entire user base every time.
 
 To calculate the exact amount of reachable users, click **Calculate Exact Statistics**. For large segments, it is normal to see slight variation even when calculating exact statistics. The accuracy of this feature is expected to be 99.999% or greater.