Sari, E., and R. . Widyasari. “Application of Hotelling T2 Control Diagram to Analyze Drinking Water Quality Control at Perumda Tirtauli Pematang Siantar City”. Mathline : Jurnal Matematika Dan Pendidikan Matematika, vol. 9, no. 1, Feb. 2024, pp. 273-84, doi:10.31943/mathline.v9i1.578.