A system may include a switchover element configurable to source or sink power from or to an electronic device electrically coupled to the switchover element and a controller in communication with the switchover element. A method for operational monitoring of weighing cells is also provided. Thus, each time a user inclines the headrest body frame section forwardly and backwardly relative to the headrest stay portions, the leaf spring element is contacted with one of the discrete flat surfaces, thereby imparting a clicking stepwise touch to a hand of the user. The back cover comprises a first side, a second side, at least one hook at the first side, and a plurality of pads at the second side.