Ginting, Heryansyah, and Edy Surya. 2017. “Development Learning Device Based for Measuring Contextual Critical Thinking Skills Students SD Class VI Mathematical”. International Journal of Sciences: Basic and Applied Research (IJSBAR) 33 (3):301-10. https://www.gssrr.org/index.php/JournalOfBasicAndApplied/article/view/7544.