M. A. Syakur, B. K. Khotimah, E. M. S. Rochman, and B. D. Satoto, “Integration K-Means Clustering Method and Elbow Method for Identification of the Best Customer Profile Cluster,” in IOP Conference Series: Materials Science and Engineering, Apr. 2018, vol. 336, no. 1. doi: 10.1088/1757-899X/336/1/012017.