A digital phase locked loop for providing clock synchronization in backplane bus systems has a loop filter with selectable high and low bandwidth modes. The rear-view mirror has a mirrow body at which is formed an accommodating member. The detection of the charging state of the battery is effected by a comparison between a current value of a current source of a differential comparator circuit and a differential output of that differential comparator circuit. The strap can secure the foot pad to the user’s skate, and generally centrally locate the foot pad over the user’s skate when the user transitions to a standing position andor a crouching position.