For any two-terminal resistive series–parallel network N with n resistors, let R : [ 0 , ∞ ] n → [ 0 , ∞ ] denote the resistance function of N . Let R |ˋ { 0 , ∞ } n be the { 0 , ∞ } -valued function obtained from R by only allowing the resistors in N to be open/short-circuited. R |ˋ { 0 , ∞ } n is a boolean function that can be coded by a boolean formula without repeated variables and no negation symbols—for short, a positive read-once formula. Let both networks N 1 and N 2 have n resistors with resistances r 1 , j = r 2 , j ∈ [ 0 , ∞ ] for each j = 1 , … , n . We prove that if R 1 |ˋ { 0 , ∞ } n = R 2 |ˋ { 0 , ∞ } n then R 1 = R 2 . We extend this result to the Wheatstone bridge.