▁the ▁effect ▁of ▁the ▁over round ▁in ▁the ▁book ▁of ▁each ▁selection ▁is ▁comp ounded ▁to ▁the ▁det r iment ▁of ▁the ▁pun ter ▁in ▁terms ▁of ▁the ▁financial ▁return ▁compared ▁to ▁the ▁true ▁odd s ▁of ▁all ▁of ▁the ▁se lections ▁winning ▁and ▁thus ▁resulting ▁in ▁a ▁successful ▁bet . ▁ ▁To ▁explain ▁the ▁concept ▁in ▁the ▁most ▁basic ▁of ▁situations ▁an ▁example ▁consisting ▁of ▁a ▁double ▁made ▁up ▁of ▁selecting ▁the ▁winner ▁from ▁each ▁of ▁two ▁tennis ▁matches ▁will ▁be ▁looked ▁at : ▁ ▁In ▁Match ▁ 1 ▁between ▁players ▁A ▁and ▁B ▁both ▁players ▁are ▁ass essed ▁to ▁have ▁an ▁equal ▁chance ▁of ▁winning . ▁The ▁situation ▁is ▁the ▁same ▁in ▁Match ▁ 2 ▁between ▁players ▁C ▁and ▁D . ▁In ▁a ▁fair ▁book ▁in ▁each ▁of ▁their ▁matches , ▁i . e . ▁each ▁has ▁a ▁book ▁of ▁ 1 0 0 %, ▁all ▁players ▁would ▁be ▁offered ▁at ▁odd s ▁of ▁Ev ens ▁( 1 - 1 ). ▁However , ▁a ▁book maker ▁would ▁probably ▁offer ▁odd s ▁of ▁ 5 - 6 ▁( for ▁example ) ▁on ▁each ▁of ▁the ▁two ▁possible ▁out comes ▁in ▁each ▁event ▁( each ▁tennis ▁match ). ▁This ▁results ▁in ▁a ▁book ▁for ▁each ▁of ▁the ▁tennis ▁matches ▁of ▁ 1 0 9 . 0 9 ... %, ▁calculated ▁by ▁ 1 0 0 ▁× ▁( ▁+ ▁) ▁i . e . ▁ 9 . 0 9 % ▁over round . ▁ ▁There ▁are ▁four ▁possible ▁out comes ▁from ▁combining ▁the ▁results