▁time ▁the ▁view able ▁impression ▁was ▁recorded . ▁This ▁data ▁results ▁in ▁a ▁visual ▁representation ▁of ▁the ▁vie wer ' s ▁environment ▁of ▁each ▁view able ▁impression ▁reported . ▁Then ▁the ▁position ▁of ▁the ▁ad ▁is ▁calculated ▁as ▁is ▁the ▁area ▁of ▁the ▁ad ▁that ▁shown ▁on ▁the ▁screen . ▁Also , ▁the ▁view ▁time ▁of ▁the ▁ad ▁is ▁collected ▁by ▁the ▁client ▁( v iewer ) ▁side ▁engine ▁considering ▁whether ▁the ▁web ▁page ▁the ▁ad ▁res ides ▁on ▁is ▁" In ▁focus ." ▁( “ In - focus ” ▁is ▁defined ▁as ▁when ▁a ▁Web ▁page ▁is ▁the ▁primary ▁window ▁open ▁on ▁a ▁user ' s ▁screen , ▁un ob struct ed ▁by ▁any ▁other ▁application ▁window . ▁Web ▁page ▁focus ▁can ▁be ▁affected ▁by : ▁minim izing ▁the ▁browser , ▁opening ▁or ▁switching ▁to ▁another ▁browser ▁window ▁or ▁application , ▁opening ▁or ▁switching ▁to ▁another ▁browser ▁window ▁tab , ▁or ▁placing ▁the ▁cur ser ▁on ▁the ▁browser ▁address ▁bar ▁or ▁other ▁browser ▁button ). ▁ ▁Lim itations ▁of ▁impression ▁method ology ▁ ▁Re asons ▁why ▁an ▁impression ▁may ▁not ▁appear ▁to ▁a ▁vie wer ▁overcome : ▁ 1 . ▁The ▁vie wer ▁clicks ▁to ▁another ▁web ▁page ▁before ▁the ▁ad ▁loads ▁and ▁rend ers ; ▁ 2 . ▁The ▁ad ▁loads , ▁but ▁in ▁an ▁area ▁of ▁the ▁web ▁page ▁that ▁is ▁not ▁within ▁the ▁vie wer ' s ▁browser ▁window ▁dimensions ▁and ▁scrolling ▁position ; ▁ 3 . ▁The ▁requests ▁made ▁by ▁sp iders , ▁craw lers , ▁web -