Kuswandi, B., Damayanti, F., Jayus, J., Abdullah, A. and Heng, L. Y. (2015) “Simple and Low-Cost On-Package Sticker Sensor based on Litmus Paper for Real-Time Monitoring of Beef Freshness”, Journal of Mathematical and Fundamental Sciences, 47(3), pp. 236-251. doi: 10.5614/j.math.fund.sci.2015.47.3.2.