An apparatus for commissioning and balancing a central heating system of the type having a boiler for heating water and a pump for pumping the water through a plurality of radiators interconnected by pipes. The liquid crystal display has at leas tone transparent portion through which the mechanical reel or reels can be observed. At a pre-charge period, the floating input stage transmits the input data to the first string of transistors; the first string of transistors stores the logic status of the input data, and pre-charges its output node to a first level.