A wrist device includes a performance measuring unit, a skin temperature measuring unit, and a processing unit. The performance measuring unit measures performance data of a user, which includes heart rate of the user measured with a pulse detector and acceleration related to movement of the user measured with an acceleration sensor. The skin temperature measuring unit measures skin temperature data of the user. The processing unit determines a fluid loss value based on the performance data, determines a relation between a predetermined perspiration threshold and a skin temperature value deduced from the skin temperature data, and determines a real fluid loss value of the user based on the fluid loss value and the relation between the predetermined perspiration threshold and the skin temperature value. An arrangement includes clothing wearable by a user and is communicatively couplable with an electronic device.
