From now on, you'll be able to practise sports or go for long walks while controlling your heart rate thanks to the watch-cardiometer with chest strap. Additionally, if you want to use it as a watch, its modern and fashionable style will look perfect on your wrist. Waterproof. Approx. maximum dimensions of the chest strap: 100 cm. Approx. minimum dimensions of the chest strap: 70 cm. The watch-cardiometer and the chest strap are battery operated (1 x CR2032 each, both included).The chest strap is made of a flexible and resistant material.