▁per ▁lead ▁( le ad ▁usually ▁meaning ▁a ▁free ▁registration ) ▁ ▁C PS ▁- ▁Cost ▁per ▁sale ▁ ▁d CP M ▁- ▁Dynamic ▁C PM ▁ ▁C PA ▁– ▁Cost ▁per ▁action ▁ ▁The ▁View able ▁Im pression ▁approach ▁enables ▁online ▁advert ising ▁effect iveness ▁to ▁be ▁analyz ed ▁based ▁on ▁stopping ▁power , ▁brand ing ▁ability ▁and ▁level ▁of ▁eng agement ▁– ▁the ▁three ▁key ▁elements ▁that ▁drive ▁purchase ▁consideration ▁and , ▁ultimately , ▁sales . ▁ ▁Having ▁no ▁reliable ▁way ▁of ▁meas uring ▁actual ▁view ership , ▁web ▁publish ers ▁are ▁vulner able ▁to ▁payment ▁methods ▁that ▁are ▁based ▁on ▁performance - based ▁advert ising ▁such ▁as ▁cost ▁per ▁click ▁and ▁cost ▁per ▁transaction . ▁ ▁Since ▁the ▁publish er ▁has ▁no ▁control ▁or ▁input ▁on ▁the ▁demand ▁and ▁ad ▁cre ative ▁quality ▁of ▁the ▁advert ised ▁product , ▁web ▁publish ers ▁lose ▁control ▁of ▁their ▁yield , ▁giving ▁away ▁significant ▁invent ory ▁to ▁ad s ▁that ▁are ▁not ▁clicked . ▁ ▁With ▁the ▁arrival ▁of ▁the ▁View able ▁Im pression ▁model ▁ ▁– ▁Cost ▁per ▁Th ous and ▁View able ▁ad s ▁has ▁emer ged , ▁quoted ▁in ▁terms ▁of ▁C PM V . ▁ ▁This ▁model ▁may ▁eventually ▁become ▁the ▁standard ▁C PM ▁as ▁it ▁measured ▁at ▁the ▁same ▁point ▁( of ▁the ▁view ) ▁as ▁television ▁or ▁print . ▁ ▁Architecture ▁Example ▁▁ ▁View able ▁Im pression ▁re lies ▁on ▁Web ▁bugs ▁( or ▁' tags ') ▁placed ▁on ▁the ▁web ▁pages ▁or ▁in ▁the ▁third -