The scientific paper Lin LI. A concordance correlation coefficient to evaluate reproducibility. Biometrics 1989 ;45:255-68. 10.2307/2532051 which has been cited 8580 times to this date: https://scholar.google.com/scholar?hl=de&as_sdt=0%2C5&q=A+Concordance+Correlation+Coefficient+to+Evaluate+Reproducibility&btnG= But a paper of the Swiss Federal Institute of Sport Magglingen, SFISM about the Polar H10 which was funded partly by Polar: «RR interval signal quality of a heart …