Fig. (6) (a) 4C-HHall with 90° symmetry. (b) Its conformal transformation w' = -j cot(π/8 + α1/2)(z - exp(jπ/4))/(z + exp(jπ/4)) has 2 electrical DoF, because W'1 = tan(π/8 - α1/2)/ tan(π/8 + α1/2), W'3 = cot2(π/8 + α1/2), and W'4 = cot(π/8 - α1/2) cot(π/8 + α1/2) are linked to a single DoF α1 and the sheet resistance Rsh is the second electrical DoF. (c) Its ERC has also 2 electrical DoF.