A navigation apparatus includes hierarchically road map data having third-, second-, and first-layer data respectively representing a high, intermediate, and low road rank. to obtain a gaseous phase comprising carbonyl sulphide, carbon disulphide and carbon dioxide. The DC bias of the floating grid is adjusted so that the ending emission phase of the electron beam from the floating grid occurs earlier than the starting phase of back-bombardment of the electrons in the RF cavity, thereby suppressing the back-bombardment of the electrons. Improved calibration is also provided for sensing and correcting for non-uniformities of rendering devices, such as color displays, printer, presses, or other color image rendering device. Such amorphous polyester chip can be obtained by cooling an amorphous polyester obtained by melt polymerization, cutting the polyester to give a chip, feeding the chip in a treatment tank, drying the chip and removing fine particles.