Geometric Inspection of Complex Numbers
Illustration showing complex numbers with a modulus equal to unity. The lines representing these numbers terminate in points lying on the circumference of a circle whose radius is unity.
George N. Bauer, PH.D. and W.E. Brooke, C.E., M.A. Plane And Spherical Trigonometry (Boston: D.C. Heath & Co., 1917) 115