A phase-locked loop circuit is used to synchronize data transfers between a fast clock and a slow clock domain. Electrically-driven dental injectors includes one having a mechanism for disengaging a pinion from a rack in order to retract a plunger rod upon completion of injection; however, it has heretofore been necessary to manually operate the operating part from outside each time. Radiation pattern of LEDs may be changed by refractive-reflective optics or by convex lenses. The method comprises the steps of: alternately supplying the container with at least a first and a second fluid respectively via the inflow, where the density of the fluids differs; and at least during an initial stage of the method controlling a flow resistance in at least one of the first and second fluids through the container.