Naksen, Puttaraksa, Plaifa Saisui, Thanaporn Chomphu, Wiphaphon Chaksuma, Wipark Anutrasakda, and Purim Jarujamrus. “Barcode-like paper sensor for water hardness detection”. Journal of Science and Science Education (JSSE) 4, no. 1 (June 24, 2021): 51–61. accessed April 12, 2025. https://so04.tci-thaijo.org/index.php/JSSE/article/view/251650.