Heart rate counter for exercise. It gives approximal rates for training. # Sources for calculations:
https://www.topendsports.com/testing/heart-rate-max.htm
https://www.topendsports.com/fitness/karvonen-formula.htm
https://www.topendsports.com/fitness/heartrate-range.htm
https://www.topendsports.com/testing/heart-rate.htm
https://vocatum.fi/sykealueet-liikunta/
