A system and method implemented by a computer for performing query based electronic document retrieval implementing a Markov process model adapted for determining a relationship or relevance between documents. A first input of the comparator is coupled to receive output codes from the ADC, while a second input is coupled to receive a sequence of target codes covering at least a portion of a range of the output codes. The system also comprises a localizer coupled to the ultrasound machine, and a display coupled to the computer for displaying the generated icon superimposed on the real-time image. The method may further include reversing the direction of rotation of the stem by sliding a slidable section of the cam with the at least one pin.