▁sheet ▁resistance ▁as ▁opposed ▁to ▁resistance ▁or ▁resist ivity ▁is ▁that ▁it ▁is ▁directly ▁measured ▁using ▁a ▁four - term inal ▁sens ing ▁measurement ▁( also ▁known ▁as ▁a ▁four - point ▁pro be ▁measurement ) ▁or ▁indirect ly ▁by ▁using ▁a ▁non - contact ▁ed dy ▁current ▁based ▁testing ▁device . ▁She et ▁resistance ▁is ▁invari able ▁under ▁scaling ▁of ▁the ▁film ▁contact ▁and ▁therefore ▁can ▁be ▁used ▁to ▁compare ▁the ▁elect rical ▁properties ▁of ▁devices ▁that ▁are ▁significantly ▁different ▁in ▁size . ▁ ▁Calcul ations ▁ ▁She et ▁resistance ▁is ▁applicable ▁to ▁two - dimensional ▁systems ▁in ▁which ▁ ▁thin ▁films ▁are ▁considered ▁two - dimensional ▁entities . ▁When ▁the ▁term ▁sheet ▁resistance ▁is ▁used , ▁it ▁is ▁imp lied ▁that ▁the ▁current ▁is ▁along ▁the ▁plane ▁of ▁the ▁sheet , ▁not ▁per pend icular ▁to ▁it . ▁ ▁In ▁a ▁regular ▁three - dimensional ▁conduct or , ▁the ▁resistance ▁can ▁be ▁written ▁as ▁ ▁where ▁ ▁is ▁the ▁resist ivity , ▁ ▁is ▁the ▁cross - section al ▁area , ▁and ▁ ▁is ▁the ▁length . ▁ ▁The ▁cross - section al ▁area ▁can ▁be ▁split ▁into ▁the ▁width ▁ ▁and ▁the ▁sheet ▁thick ness ▁. ▁ ▁Upon ▁combining ▁the ▁resist ivity ▁with ▁the ▁thick ness , ▁the ▁resistance ▁can ▁then ▁be ▁written ▁as ▁ ▁where ▁ ▁is ▁the ▁sheet ▁resistance . ▁If ▁the ▁film ▁thick ness ▁is ▁known , ▁the ▁bulk ▁resist ivity ▁ ▁( in ▁ Ω · cm ) ▁can ▁be ▁calculated ▁by ▁multip lying ▁the ▁sheet