▁was ▁actually ▁visible ▁to ▁a ▁vie wer . ▁ ▁Over view ▁ ▁With ▁the ▁development ▁of ▁the ▁first ▁ad ▁servers ▁in ▁ 1 9 9 5 – 1 9 9 6 ▁the ▁assumption ▁was ▁that ▁a ▁requested ▁ad ▁was ▁always ▁available ▁to ▁the ▁vie wer ▁of ▁a ▁requested ▁web ▁page . ▁This ▁allowed ▁for ▁the ▁util ization ▁of ▁the ▁server ▁log ▁file ▁for ▁collection ▁of ▁metadata ▁to ▁deliver ▁a ▁metric ▁called ▁the ▁Online ▁Im pression ▁that ▁in ▁traditional ▁media ▁meant ▁an ▁impression ▁on ▁a ▁vie wer . ▁ ▁This ▁type ▁of ▁advert ising ▁metric ▁was ▁meant ▁to ▁res emble ▁Television ▁and ▁print ▁advert ising ▁methods ▁for ▁spec ulating ▁the ▁cost ▁of ▁an ▁advert is ement , ▁with ▁the ▁promise ▁of ▁even ▁more ▁accuracy ▁due ▁to ▁the ▁interactive ▁nature ▁of ▁the ▁Internet ▁elimin ating ▁the ▁need ▁for ▁industry - accept ed ▁approxim ates ▁such ▁as ▁N iel sen ▁ratings ▁for ▁television ▁and ▁circul ation ▁figures ▁for ▁print ▁publications . ▁ ▁The ▁value ▁of ▁an ▁ad ▁tradition ally ▁was ▁based ▁upon ▁an ▁estimate ▁of ▁how ▁many ▁different ▁people ▁saw ▁or ▁heard ▁the ▁ad . ▁The ▁following ▁are ▁current ▁accepted ▁means ▁of ▁calculating ▁C PM ▁for ▁different ▁medium s : ▁ 1 . ▁C PM ▁for ▁print ▁media ▁( when ▁audience ▁data ▁is ▁available ): ▁▁ 2 . ▁C PM ▁for ▁broadcast ▁media : ▁ ▁With ▁the ▁advent ▁of ▁the ▁Internet , ▁through ▁log ▁file ▁server ▁collect ing ▁data ▁it ▁was ▁believed ▁that ▁ad ▁views ▁could ▁be ▁track ed ▁with ▁un pre ced ented ▁accuracy ▁and