“…It turns out that that the transformation of the axis systems that yields Eq. (4) is equivalent to one of the six standardization transformations denoted S1 to S6 utilized in the orthorhombic standardization [42,43]. Importantly, the orthorhombic standardization yields six alternative orthorhombic ZFSP sets for all ranks (k ¼2, 4, 6) for transition ions, which are physically equivalent yet numerically different.…”