of the current i p or respectively i p1 and i p2 induced on the unit under test by the plasma is likewise not metrologically possible r schicht must therefore be indirectly determined when the relationships r m1 r m2 r m and i p1 i p2 are valid in the circuit equation 11 is simplified to u sub a u sub b u sub sa u sub sb r sub sa i sub m r sub sa i sub p1 r sub sb i sub m r sub sb i sub p2 13 upon assumption of the relationships r sa r sb and i p1 i p2 equation 13 is simplified to with the assistance of equations 12 and 14 and with u m1 r m1 i m r schicht is calculated as r sub schicht u sub a u sub b i sub m u sub a u sub b 1 2 u sub m1 u sub m2 r sub m 2 u sub a u sub b r sub m u sub v1 u sub a u sub b u sub v2 15 since u m1 u a u v1 0 and u m2 u v2 u b 0 are also true as in the undisturbed case thus the measurement of the sheet resistivity is based on a voltage measurement 4 u00d7 single ended to ground or 2 u00d7 differentially at r mx and at the unit under test the influence of the.