An Indicator that visually signals when it is time to start and stop watering by the Indicator’s ability to distinctively change it’s relative physical size andor shape as it takes on and releases the water. The approach permits the display to be activated during the warm-up process. An excitation voltage corresponding to the mass-to-charge ratio of the objective ion is applied to end-cap electrodes 3 and 4 to cause an oscillation of the objective ion and help dissociation of the ion by CID. The third component is formed so as to have a second mating structure which is adapted to mate with the second locating construction in the first component so as to uniquely locate the third component with respect to the first component. Therefore, it is possible to achieve an optical coupling with high accuracy in mounting a light emitting device on the pedestal block.