Before revision: must be calculated with respect to the axis which is perpendicular to the applied loading and which passes through the centroid of the cross section .For an Euler–Bernoulli beam not under any axial loading this axis is called the neutral axis.
After revision: must be calculated with respect to the axis which is perpendicular to the applied loading .For an Euler–Bernoulli beam not under any axial loading this axis is called the neutral axis.