A method of producing cementitious mixtures containing fly ash as one of the cementitious components, under air entrainment conditions. During a configuration procedure, all the configuration symbols are electro-optically scanned and decoded, and the symbol sequence number, the total number of the configuration symbols, and the fractional amount of the keyboard layout data are extracted for each configuration symbol. Therefore, the false diagnosis of the EGR system can be avoided with a simplified process without requiring specific determinations on individual abnormal states of the various components other than the EGR system. The display board may have a generally rectangular shape and may include a plurality of corner members and a mounting structure. At least one of the plurality of regions is selected. The binaural output includes the full-bandwidth of the microphone output signals.