Prachumkayohmat, N., C. Manakarn, R. Chariyamakarn, Y. Srisawat, and N. Umar. “The Nature of Mathematical Conceptual Understanding of Grade 6 Students on Weight Measurement Based on APOS Theory”. Pridiyathorn Science Journal, vol. 2, no. 2, Mar. 2024, pp. 43-57, https://li04.tci-thaijo.org/index.php/psj/article/view/2005.