Maulana, A., M. Yunus, and D. Sulistyaningrum. “The Constructions of Egg-Shaped Surface Equations Using Hugelschaffer’s Egg-Shaped Curve”. Indonesian Journal of Physics, Vol. 26, no. 2, Dec. 2015, pp. 26 -30, doi:10.5614/itb.ijp.2015.26.2.2.