This is a sample Google has put forward to understand about the changes it has made to average ranking position of pages in a site.

“Let’s say Adam searched for [blue berries] and URLs from your site appeared in positions 3, 6, and 12. Richard also searched for [blue berries] and URLs from your site appeared in positions 5 and 9. Previously, we would have averaged all these positions together and shown an Average Position of 7. Going forward, we’ll only average the highest position your site appeared in for each search (3 for Adam’s search and 5 for Richard’s search), for an Average Position of 4.” There won’t be any changes made to historical data.