The invention provides a heart rate monitor, a method and a computer software product. The method determines (702) from the users electrocardiogram a reference value of a heart rate variable characterizing the heart rate determines (704) at least one environmental parameter value obtainable from air pressure using air pressure measurement associates (706) the reference value of the heart rate variable with at least one environmental parameter value and records (708) in a register at least one environmental parameter value and the reference value of the heart rate variable associated with the at least one environmental parameter value.
