This is a diagram drawn by Maurice to illustrate the use of the Watt Linkage in the lever mechanism.  the Watt Linkage was designed and built by James Watt to restrain the movement of a steam engine piston to as straighter line as possible.  This would increase efficiency of the piston and reduce wear.  Mechanism based upon the Watt Linkage are currently used in some racing car suspension, and indeed, in this press.  It is a very efficient way to transfer energy and power and thus perfect for maximising the pressure transference from printer pulling the lever to pressure being exerted onto the plate.