A sheet folding apparatus includes a fold unit which folds a center of a sheet bundle to form a fold line, and a reinforce roller which moves along the fold line while applying pressure to the fold line to reinforce the fold line. The openings have sockets with exterior gear teeth. The plate member covers the bag pressure release mechanism when the airbag is in a deflated state. Each latching member includes a second transmission portion and a lock receiving portion. One embodiment of the method comprises receiving metrology data from one or more metrology sensors; writing at least part of the metrology data to a volatile memory; incrementing a write pointer to indicate the metrology data contained within the volatile memory; and repeating the above until a timer expires, then reading at least a portion of the metrology data from the volatile memory. The complementary amplifier may have an approximately constant total input capacitance and an approximately constant total transconductance over a range of voltages.