measured at the same two scalp locations but after reversing the assignment of ‘active’ and reference site, a positive potential measurement is obtained (Fig. 1B). Other than the reversal in sign, this positive potential has the same absolute value as the previously measured negative potential, and both measurements are equally valid representations of the underlying current dipole. Moreover, the direction (or sign) of the relative difference between the two recording sites is entirely unaffected by selecting either one as the reference (i.e., E1 - E2 = -[E2 - E1]).
