Impressions aren't calculated by finding 60% of your total pageviews. Basically, an ad impression is counted every time a reader is able to see an ad on his screen. Sometimes people visit a page but don't actually scroll down far enough to see the ad. I believe that when people block ads (as with AdBlock), no impressions happen, either.
The 60% factor means that of the money generated by the impressions of your ads, 60% is shared. But the 60% has nothing to do with how many of your pageviews actually lead to ad impressions.
Kind of confusing, but I hope this helps!