The present invention provides an apparatus and method for threading a biopolymer through a nanopore. Image data is generated in response to radiation received from a field of view encompassing sheet media edges of individual media within the sheet media stack. The straps 22, 24 prevent shifting of the helmet 20 during use. A conductive tape electrically connects between the touch screen electrode and a driver circuit. The light projection system can include a light intensity sensor in an image path, in a light-source subsystem light-dump path, in a light-modulation subsystem light-dump path, in a position to measure light leaked from optical components, or combinations thereof. The subset formed by identifying similarities and differences of the values between the virtual machine images.