Suppose you display 2 leaderboards. 1st leaderboard shows 400 ad impressions and 2nd one shows 300 ad impressions. It might be like the 1st leaderboard showed all 4 ads 100 times, and 2nd leaderboard showed 3 ads only all 100 times... So...there is a difference.. Now this is randomly done okay? The above was an example as to how it might differ.