Zuraini, H. H. M., W. Ismail, R. Hendradi, and A. Justitia. “Students Activity Recognition by Heart Rate Monitoring in Classroom Using K-Means Classification”. Journal of Information Systems Engineering and Business Intelligence, vol. 6, no. 1, Apr. 2020, pp. 46-54, doi:10.20473/jisebi.6.1.46-54.