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The spectrum of a frequency-limited periodic wave may be obtained rapidly by measuring its truncated Walsh spectrum, and then converting from Walsh spectrum to Fourier spectrum after the measurement. The conversion process consists of a matrix multiplication in which a measured Walsh spectrum vector, of dimension 2k, is multiplied by a 2kX 2kconversion matrix that is compensated for Walsh-spectrum truncation, to yield the corresponding Fourier spectrum vector. The microprocessor is well suited to this end; it is also useful in monitoring instrument panel switches and driving a display and print-out. This paper compares available microprocessors from the viewpoint of BCD processing—and concludes that the Fairchild PPS25 processor is the one best suited to meet the requirements.