This power pack has smooth speed control for gentle starts and power increases in speed up to the maximum speed. It also has single-knob operation for setting the voltage in the track and for changing the direction of travel by turning the control knob away from the center position. Power pack dimensions 130 mm (L) x 70 mm (W) x 50 mm (H) / 5-1/8" (L) x 2-3/4" (W) x 2" (H).