A tunnel notcher and guidewire delivery device is provided for creating a notch and positioning a guidewire within a bone tunnel. Extra or missing horizontal lines are processed using modulo or digital phase lock loop-type circuit to change clock output signal proportionately according to a difference determined by comparing a standard video signal value with an actual input signal line count value, such that modified clock output signal serves as a clock input signal for circuit accepting standard video format. The pressing surfaces are opposed to one another and operable to compress a quantity of the material therebetween. In one implementation, the display of the categories and information on the user interface is handled by the main thread and the retrieval of the data associated with the chosen category is performed by a worker thread executing asynchronously with respect to the main thread. Alternatively, or in addition, the determination can be based on a template, which may be indicative of an instrument response of the interferometer used to obtain the low coherence interference signal.