Chittrakarn, P., T. Intidach, M. Koonjaethong, N. Dawnvongyad, and N. Kunawaradisai. “Standard time in outpatient dispensing service using stopwatch time technique”. Asia-Pacific Journal of Science and Technology, vol. 17, no. 3, Apr. 2017, pp. 493-04, https://so01.tci-thaijo.org/index.php/APST/article/view/83262.