Energy characteristics as the load power and efficiency via the load resistance are the well-known two-valued cubic curves. The consideration of these quadratic fractional expressions as geometric projective transformations makes it possible to introduce the cross ratio of four points in limited single-valued working areas. The cross ratio is accepted as the regime parameter in a relative form, which is invariant to a type of the actual regime parameters and circuit sections. The form of expressions for the actual parameter changes depends on the actual regime type. Changes in regime parameters are proved; direct formulas of recalculation are proposed.