Why goggle page impressions is not matching with my site counters?

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I am really confused who are true. Today my counters say that 60 unique visitors visit my site http://bdsurf.co.cc for 268 times .But when I check my adsense account it showed me that today I have get only 15 page impressions. By how it is possible. Its not the matter of today but is occuring from my joining in adsense always my page impressions is very few. I am now using two different counters & both are showing same. Then what is the actual measurement to calculate page impressions in google adsense?