As we sah the papers about the Polar OH1 tested with a g.tec g.Nautilus multipurpose device which costs 50 000 USD: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0217288 and two papers written by cardiologists from the Cleveland Clinic in Ohio about consumer grade heart rate monitors: https://journals.lww.com/acsm-msse/Fulltext/2017/08000/Variable_Accuracy_of_Wearable_Heart_Rate_Monitors.22.aspx https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6732081/ We where very happy about those. Finally we had found what we where …