Ulbikas, J., A. Čenys, D. Žemaitytė, and G. Varoneckas. “Correlation in the Heart Rate Data”. Nonlinear Analysis: Modelling and Control 2, no. 1 (December 21, 1998): 141–148. Accessed July 6, 2025. https://www.zurnalai.vu.lt/nonlinear-analysis/article/view/15301.