Defined by \[G^{\sigma }=H^{\sigma }- T\ S^{\sigma }=A^{\sigma }- \gamma \ A_{\text{s}}\] where \(H^{\sigma }\) is the @[email protected], \(T\) is the @[email protected], \(S^{\sigma }\) is the @[email protected], \(A^{\sigma }\) is the @[email protected], \(\gamma \) is the @[email protected], and \(A_{\text{s}}\) is the area relative to a @[email protected]