Chong, Kim Soon, Kok Beng Gan, and Mohd. Ali Mohd. Alauddin. 2013. “Development of a Two-Channel Simultaneous Photoplethysmography Recording System”. Journal of ICT Research and Applications 6 (2):171-82. https://doi.org/10.5614/itbj.ict.2012.6.2.5.