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Dear editor,rnThe technical limitations on sensors mean that some state variables will not be detected in any controlled system,so the actual values of an output function will always deviate somewhat from the nominal values.A practical example was given in[1],where the output of an infrared sensor that measures the distance between parts in a magnetic bear-ing suspension system suffers from measurement error[1].Such systems require a novel approach for finding the ef-fects of measurement error in global output feedback stabi-lization[2-5].However,as pointed out by[1],unknown non-linearities hinder the design and analysis of output-feedback control strategy,and as a result there are many unsolved problems that are worth studying from theoretical as well as practical perspectives.