where formula_10 is the current at a height of formula_11 electrical degrees above the ground, and formula_12 is the maximum current. At heights of a little less than a multiple of a quarter wavelength, formula_13 ...(G = 90°, 180°, 270°...) the mast is resonant; at these heights the antenna presents a pure resistance to the feedline, simplifying impedance matching the feedline to the antenna. At other lengths the antenna has capacitive reactance or inductive reactance. However masts of these lengths can be fed efficiently by cancelling the reactance of the antenna with a conjugate reactance in the matching network in the helix house. Due to the finite thickness of the mast, resistance, and other factors the actual antenna current on the mast differs significantly from the ideal sine wave assumed above, and as shown by the graph, resonant lengths of a typical tower are closer to 80°, 140°, and 240°.