One question which often arises in feedback systems is how often should one sample to know the options with which control adjustments may be made. In an optimal control scheme. we suppose that a control arrangement will be employed in which the sampling interval ishunits long wherehis an unknown integer. The equations describing both the dynamics and the noise process now depend on this intervalh. Now considering the noise process and the cost and frequency of sampling, a reasonable cost function is formulated as a function ofh. The optimum time interval at which surveillance should be conducted, i.e. observations taken and control adjustment action taken, is obtained by minimizing the above cost function.