Setyaningrum, Ika Rizky, and Palti Marulitua Sitorus. “Efficiency Measurement of Maintenance Costs on Customer Service Process PT Indonesia Comnets Plus West Java”. TRIKONOMIKA : Jurnal Ekonomi, vol. 14, no. 2, Dec. 2015, pp. 138-42, doi:10.23969/trikonomika.v14i2.411.