▁( 1 9 3 8 ) ▁cover ▁board ▁was ▁ 6   fe et ▁in ▁height , ▁marked ▁and ▁number ed ▁every ▁foot . ▁Vis ible ▁marks ▁were ▁counted ▁to ▁measure ▁obst ruction ▁by ▁plants . ▁Kob r iger ▁( 1 9 6 5 ) ▁developed ▁a ▁ 4 × 4 - foot ▁board ▁marked ▁at ▁ 3 - inch ▁intervals ▁with ▁altern ating ▁white ▁and ▁black ▁squares . ▁He ▁placed ▁a ▁camera ▁in ▁the ▁center ▁of ▁the ▁bre eding ▁ground ▁at ▁a ▁height ▁of ▁ 3   fe et . ▁He ▁then ▁placed ▁the ▁cover ▁board ▁ 3 0   fe et ▁away ▁taking ▁photograph s ▁of ▁the ▁cover ▁board . ▁After ▁compiling ▁all ▁the ▁photograph s , ▁they ▁were ▁analyz ed ▁with ▁a ▁hand ▁l ens ▁to ▁assess ▁the ▁number ▁of ▁squares ▁visible . ▁This ▁number ▁gave ▁him ▁a ▁veget ation ▁index ▁of ▁cover ▁classes . ▁This ▁method ▁has ▁been ▁modified ▁by ▁Lim b ▁et ▁al . ▁( 2 0 0 7 ). ▁Instead ▁of ▁taking ▁photograph s ▁ 3 0   fe et ▁away ▁like ▁Kob r iger ▁( 1 9 6 5 ), ▁Lim b ▁et ▁al . ▁( 2 0 0 7 ) ▁took ▁photograph s ▁of ▁veget ation ▁back - dro pped ▁by ▁a ▁ 1 × 1 - meter ▁cover ▁board ▁at ▁a ▁height ▁of ▁ 1   meter , ▁ 4   met ers ▁away . ▁These ▁digital ▁photograph s ▁were ▁uploaded ▁to ▁Ad obe ▁Ac ro bat ▁and ▁digit ized ▁to ▁the ▁ 1