A state of storage of a memory cell is determined based on the capacitance stored in capacitor, and the memory cell includes a transfer gate transistor, a capacitor and first and second inverters cross coupled with each other. The method further includes selectively charging and discharging a second conductor with a second set of p and n element-pairs in response to a voltage potential applied to the second set of p and n element-pairs. Therefore the indirect cause of a fire is removed and the maintenance work simplified. A quad wedge optical device separately redirects diffraction orders of radiation scattered from the substrate and separates diffraction orders from illumination along each of the first and second directions. The method provides using screws having a screwing rotation direction contrary to the rotation direction of the rotor.