## 2 State of Art
### Studies on Customer Satisfaction Evaluation
It is widely used in sectors such as manufacturing, services, healthcare, and finance, helping organizations optimize processes, reduce costs, and enhance customer satisfaction. The study sought to sustain and maintain accreditation, protect consumer health by preventing disease outbreaks, and facilitate continual improvement of the system. The findings reveal that brainstorming teams successfully identified bottlenecks and wastes contributing to customer dissatisfaction. These wastes were the root causes of the laboratory's inefficiency and failure to meet service level agreements with customers. The application of lean six sigma tools was successful, as the accurate selection and implementation of appropriate tools led to noticeable improvements in laboratory performance. [PERSON] et al. [21] conducted a study aimed at identifying indicators and analyzing customer satisfaction performance at a local water company in Muara Enim Regency, South Sumatra Province, Indonesia. The evaluation of services was based on the timing of water distribution and the quality of the delivered clean water. Customer satisfaction in this study is defined as individuals' feelings after comparing their experiences with their expectations. The study assessed customer satisfaction using criteria such as tangibles,reliability, responsiveness, assurance, and empathy. Three key strengths identified for improving customer satisfaction include the extensive water distribution network, high-quality staff service, and the experience of staff and technicians. These strengths can be leveraged to address potential weaknesses, such as low water discharge, poor water quality, infrequent streaming, and short duration of water flow. However, to ensure that the existing strategies are effective and meet the planned objectives, it is also crucial to focus on optimizing processes and minimizing threats. [PERSON] et al. (2018) emphasize the workforce challenges in environmental laboratories, noting the necessity of effective management to lead laboratory staff and meet the stringent requirements of analyzing samples critical for public health and environmental protection. According to the authors, an environmental laboratory can utilize metrics such as customer satisfaction with treated water to monitor customer feedback over time. If the data indicate that customers are not entirely satisfied, the laboratory can review and refine its processes to enhance customer satisfaction. The studies reviewed highlight the critical role of service quality, organizational culture, and effective management systems in enhancing customer satisfaction within laboratory settings, particularly those accredited to ISO/IEC 17025. Across various sectors, including water testing, calibration, and environmental laboratories, high service quality is consistently linked to greater customer satisfaction, which in turn drives operational efficiency and economic improvement. Lean six sigma and robust laboratory quality management systems emerge as effective tools for identifying inefficiencies, ensuring reliable results, and fostering a culture of continuous improvement. Overall, improving service quality, optimizing processes, and addressing customer feedback are pivotal strategies for laboratories to maintain accreditation, protect public health, and enhance customer satisfaction.