PPG devices – Page 375 – PETER GAMMA (Director & Physiologist), MEDITATION RESEARCH INSTITUTE SWITZERLAND (MRIS)

g.tec medical device which was used as reference device to test the accuracy of the Polar OH1 had active electrodes, which are very expensive and reduce ECG motion artifacts, still tests on the treadmill were only performed at slow speeds

PLOS ONE paper: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0217288 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6732081/