A method includes producing first data in a page region of a memory, the first data including a first number of memory sets, each of the memory sets having a second number of bits, where the first number is a positive number more than one and the second number is a positive number more than three. The display apparatus comprises a light source and an optical compound layer, wherein the light source is adapted to emit a light beam, and the light beam has a polarization direction. Said immobilizing device is adapted to be introduced into said slot through said loading window and comprises a locking element arranged in a space separating two adjacent blade roots. The range in which the focal length can be varied depends on the diameters of the holes, and giving the holes of the different electrodes varying diameters helps widen the range.