I used my first Polar watch it 20 years ago. The product has evolved. Both batteries can be changed easily by turning a small cover with a coin. Before the transmitter battery (belt) was impossible to change and that of the easily watch. New features, possibility to introduce his age, weight and height for the watch define itself on the user profile and the pulse range to meet. Only small areas for improvement perhaps, having to play a lot with the buttons to view all (heart rate -> Time -> Training duration -> energy expended). The figures could be a bit more readable (strong square figures as the displays of the 80s). Its quite small. But these are details. Otherwise, it's a great product.