A positioning control device and method in which the relative position error in tracking is reduced by using the periodicity of position shift. The vessel has a wall structure through which a mounting bore extends. The values within the two categories are then summed, with the resultants potentially modified using a series of one or more equations. The sliding mechanism is arranged between the cover unit and the base unit in order to guide the relative sliding between the cover unit and the base unit. Additionally, the user-selectable list box may disappear or no longer be displayed in response to a user interaction outside the user-selectable list box, in response to a selection of an item from the user-selectable list box, etc. The device may determine the level of blood constituent, may use this level for monitoring andor to activate an alarm when the level falls outside a predetermined range, may be applied to monitoring conditions of apnea, respiratory stress, and reduced blood flow in organ regions, heart rate, jaundice, and blood flow velocity, and may be incorporated within a monitoring system.