A reprographic marking device has two rolls, e. The guiding channels may have laterally disposed rollers or else be made of slick material to allow the helicopter to slide towards the base of the guiding channel under the helicopter’s own weight. The engaging members detachably engage with corresponding elastic arms whereby the supporting member is detachably engaged with the base. The data processing system includes a processor module. The power-saving circuit collects charges from an equivalent load capacitor of each data line, before the output buffer stage drives the two adjacent data lines through the positive and negative output channels.