Hakim, Sulton Nur, Alfatah Kalijaga, and Sri Indrawati. “SERVICE PERFORMANCE IMPROVEMENT DURING PANDEMIC COVID 19 USING INTEGRATED SERVQUAL AND SIX SIGMA: TELECOMMUNICATION AND INFORMATION INDUSTRY CASE APPLICATION”. Journal of Industrial Engineering and Halal Industries 1, no. 2 (December 31, 2020): 94–101. Accessed February 1, 2025. https://ejournal.uin-suka.ac.id/saintek/JIEHIS/article/view/2198.